For large mods that add numerous NPCs with custom dialogue, what does everyone do about the voices? I know some have no voices, and use the silent sync thing instead, and I've seen a couple that had voice acting (although it sounded really out of place). Is there an alternative for getting (more-or-less) Bethesda-sounding voices with your dialogue?

Back a couple years ago, there was a Voice Actors Guild or something similar - is that still around? And is it still a viable option?

http://tesalliance.org/forums/index.php?/forum/74-voice-actors-project/
I'm sure there's others.

Voice acting is much more difficult than most people imagine. Mimicing another actor's characterization is even morre difficult. Some of it is talent, but there are other factors such as quality of recording equipment and post recording mixing software.

Not that you are asking this, but just for FYI, getting the original Bethesda actors to do mods is out of the question unless it's under a union contract and they get paid. And that's never going to happen because the paperwork is too much of a pain and the cost is too high.

Best chance at getting good voice acting is recruiting talented non-uinion actors who are looking for experience to develop for their voice over demo reel. But you also still need high quality recording and mixing gear / software in order to do anything with it.

In terms of software/hardware you can get this relatively inexpensively with a copy of Reaper recording software and a decent Firewire audio interface - I use pretty much this setup for recording/mixing music and it works just fine.
The most important things from this point of view I would suggest are a decent knowledge of HOW to mix and produce vocals and a good quality, appropriate microphone plus some idea of where to put it, location-wise, for the best sound.

A competent voice-actor is difficult to find; it's not just talking into a microphone - (obv) - but knowing HOW to put your voice across and how to interact with the microphone - without even thinking about putting some characterisation into the game itself - otherwise it just comes across as wooden which is actually more immersion-breaking than no voice at all. It's also very time-consuming and quite dull and takes a lot of commitment...

...imho...

I guess the question is what you mean by "high quality"... If you want a professional result, you of course need professional equipment.
Myself, I have been recording in Audacity with an ordinary headset and some patience. I don't by any mean claim that what I have done is "professional" or even "good", but as quite a few players seem to find my voiceacting for Companion Vilja sufficient, I guess I have achieved a, well, reasonable, result with very basic equipment and zero experience.

So, guess what I want to say is that maybe one shouldn't get too discouraged by lack of expensive professional equipment.

Time-consuming and dull? Dunno... time-consuming for sure, in particular to lipsync the voicefiles, but at least I have had quite fun with the approx 6000 entries I have (so far) recorded for Vilja.

Funnily enough enough, and without being in any way creepy, I was going to cite you/Vilja as an example of voice acting done very nicely indeed!

Well, I guess it couldn't hurt to break it down some:

Talent:
Some folks have it, and are naturally good voice actors with no training. But there is a knack to make the voice sound interesting enough to catch the listener's attention, but also to be able to convey a sense of character and purpose in addition to the information as dictated by the script. There any number of ways to deliver a line, and the entire meaning of the same line can change depending on which word(s) are stressed above the others. To be convincing, conveying an emotional element is key, and it is normally difficult to express an emotion you aren't actually feeling. The big five most difficult emotions are anger, love, joy, sorrow, fear. Those are very difficult to convince others you are feeling those emotions when you actually aren't. However, in my experience, most people are usually naturally good at pretending one of the five - some folks can cry on cue, others are totally believable when they laugh (even if it isn't funny), my particular strength is numerous wasy to express anger when I'm not at all angry. However, it is not easy to be good at all of them. The more difficult a particular line is, the more recording "takes" are required in order to get it just right. Having a really good director on hand to give feedback on the recording session can help, or lacking that, someone who has some decent judgement and can at least give honest "that works/doesn't work" feedback. It's not easy, and it requires patience, but if you enjoy doing it, you should do it.

Recording environment:
This factor is usually overlooked, and can be devastating combined with a low-end microphone, and maybe doubly so if you have a really good microphone, because it is likely to pick up everything - the sound of the refrigerator/air conditioner/tv/fan, or even the hum of say a fish tank motor, or even the hum of the computer itself. You want a nice quiet space, with minimal echo, windows closed, and any unnecessary electronics turned off. Living near an airport is the worst possible curse you could wish on a sound man. If you can afford renting a professional recording studio, I highly recommend it, as they will have all the gear and a technition usually comes with the rental fee.

Headphones:
The better the headphones, the better your ability to pick out background noise and other distortions, as well as the quality of the recording.

The Microphone:
Of all the pieces of hardware, it is the most important. It doesn't matter how good the rest of your gear is, a bad mic is going to pass on bad sound. Good microphones for voice overs run $100 - $200 US dollars. Professional studios and singers can easily spend several thousand dollars on a single microphone. USB microphones are pretty much only designed to capture the voice well enough so that the other person can understand what you are saying, but don't count on them delivering a consistent crisp clean sound. Also, just because a microphone costs a lot of money doesn't mean it's actually any good. Do the research, and check out websites that target professional singers / musicians / voice over artists to see what their recommendations are.

Pop screens:
A pop screen is an attachment that is between the microphone and the mouth, and helps soften pops from hard "P"s as well as hard "S"s and "T"s. Without it, you could get a spike in the recording that goes beyond what the microphone/hardware/software can handle and you end you with crackle and distortion. You can create your own home made pop screen with some coat hanger wire and a cut up thin dress sock or panty hose, or you can just put the sock/hose over the microphone itself.

Hardware:
Most computers have built in high-def audio cards in the mother boards, and are suitable enough for voice recordings. If you want to capture musing/singing, it's worth investing in a higher end audio card.

Recording Software:
Audacity is a fairly good piece of software for capturing the recording (especially considering it is free/shareware). For more advanced recording options that allow you to use limiters and other features to control the initial quality of the recording, higher end software such as Pro-tools or Sonar are helpful for getting a clean sound off the bat.

Post-recording Software:
To add echo, pitch shifting, and use tools to edit/splice sound clips together, including blending, volume control, cleaning out pops and clicks, and eliminating cycle hum and background "white noise", the higher end software is usually more suited to the task.

It's definitely time consuming, and requires patience. Recording 100 words of dialogue and getting them "just right" could easily take a half hour to an hour, depending on how picky you are about the result. I am very self-conscious about my work, so it takes me forever, so I rarely do it unless I am passionate about it.

But then, that's what it comes down to. Regardless of what gear you have or your experience, if you are passionate about it, just do it!

And here are a few more sites that offer voice acting:

http://voiceacting.proboards.com/
http://voiceactingalliance.com/board/forum.php
http://z4.invisionfree.com/wayhouse/index.php?act=SC&c=5

We also have a couple of professional or semi-pro voice actors on http://www.darkcreations.org/forums/forum/133-voice-acting/, but so far our list is small, so they wouldn't serve for large projects.

I really appreciate all the comments - this will be my first foray into this area of modding, so I can use all the advice I can get.