I am level 30, have completed all of the marked main and side quests, and have completed all of the add ons. I have 100% of the achievements too. I want to find a way to occupy my time before New Vegas comes out. Which unmarked quests are worth doing and what location must I travel to to begin them?

http://www.google.co.uk/search?sourceid=navclient&ie=UTF-8&rlz=1T4ACPW_en___GB356&q=officius#hl=en&rlz=1T4ACPW_en___GB356&&sa=X&ei=mFiMTJPHMsLAswb4y92WAg&sqi=2&ved=0CCAQBSgA&q=officious+definition&spell=1&fp=6f4515cf04785e87 to a list of all quests including the unmarked ones.

Personally I would recommend doing (if you haven't already done them) - 'Council Seat' for the Deathclaw Schematic, 'Jiggs loot' for the Xuanlong rifle, and 'Keller Family Refuge' for the Experimental MIRV. The other quests are for caps mainly, but a few give mini-nukes and stuff.

I will say though that the unmarked quests are more like nice little bonuses as you go through the game, usually in the midst of other quests. I tried doing a load of them after I had finished with all other quests and found it quite tedious. Some, if not a lot of them will just seem pointless at the end of the game when you have loads of caps, ammo, and no need for your karma to change, but you may find some that are fun to do.

That link led me straight to google not to the wiki.

My apologies. http://fallout.wikia.com/wiki/Fallout_3_quests