Are there any mods that add marriage partners? Especially within the races/genders not in the vanilla game (Khajiit, Bosmer, male Altmer...)?

Theres Interesting NPCs and most follower mods have a ability to marry

You'll also get a few hits through the Skyrim Nexus search bar for marriage options as well, using the word "marriage" in the search bar of course.

Although you'll probably have to wait until tomorrow to do that because the Nexus is pretty much down today, either because their servers are too full or because they're under another DDoS attack. You ain't going to be downloading much of anything from the Nexus today.

Actually, this week isn't going to be a good week to be downloading mods from the Nexus because they're going to be working on http://skyrim.nexusmods.com/news/342//? to a new cluster setup due to the DDoS attacks and general server overloads that have been plaguing the Nexus lately, so I highly recommend maybe waiting until after the transfer is complete.