What are your favourite side quests?

Like the topic says, I'm wondering which side quests you liked the most. The question obviously brings RPGs to mind, but it can be any optional mission which has nothing or very little to do with the main story of the game. For the sake of those who haven't played the game, please provide a description of the quest in your answer as well as why you liked it so much (original, interesting gameplay/story, phat l00t, well crafted, just fun...). Also, since it's only a side quest, spoilers are ok!

I think i just like sidequests in general. Sure, they can get repetitive, but still, i'm not sure why, but i enjoy them.
A lot of the activities in Saints Row 2 are fun, I think Fuzz was one of my favourite. Sure it was repetitive, but it stayed fun and humorous for me.
I can't remember a specific side quest, but i enjoyed the sidequests in KOTOR1 where you had to make moral choices. At the time, moral choices in games hadn't become the new trend, so yeah, i loved those.

Recently the drug dealing in Chinatown Wars has really grabbed me

The kind that come in $10 packs for Fallout 3.
I wish Bethesda would make more. I would keep playing that game forever.

" If they have an affect on gameplay, the better they are "

I agree with both the Fallout 3 and Chinatown Wars statements. I also don't mind more inane side quests like fetch quests as long as there are a lot of enemies to fight (Fable 2) or some cool loot to collect.

I forget the name, but the one where you jump into the painting in Oblivion really took me by surprise. It's certainly the first one that comes to mind. 
 
It wasn't special gameplay-wise, and really added nothing to the broader scope of the game. But I was impressed at the curve-ball the game threw me at that point.

I hate side quests. I hate them all.

I like doing the missions for the weapons dealers in Far Cry 2. There is nothing like staking out behind a tree or a rock, waiting for a convoy to come along while you've planted some C4 on the ground... then BOOM! The enemies are so confused :p 

Basically any side quest besides fetch quests. Those are the worst.

I really dug Reillys Rangers in Fallout 3, and Wasteland Survival Guide. Honestly all the side quests in Fallout 3 are pretty good, i enjoyed those more than i did the main story. 
 
Also the side quests in KOTOR where really good.