Man I'm embarrassed to say this is practically a science with me. I have decided the optimal seat on everything I ride for the most part so here's a list of a few that everyone mentioned:
EE - Back Row. You get a bit more on the final drop, although I recommend a little closer so you can see the drop better too.
BTMRR - Gotta be the back. That ride is 10 times better in the back.
RnRC - The front is always nice. You _have_ to get an odd numbered car though if you're tall. Otherwise you can't slouch because there's not as much leg room and the shoulder restraints bite.
Splash Mountain - I prefer the front, largely because you can 'see the drop coming' at the end and get more of a sense of anticipation.
Soarin' - Gotta be the front for the reasons Imagineer said.
ToT - I really like the front because it makes me feel more alone on the ride so it's a bit more spooky. I have found that I feel the vertigo on the drop a bit more in the back though so I'm not that picky on this one.
Space Mountain - _HAS_ to be the front.
I have some more but I'm feeling a bit like a fanatic now, so I think I'll let someone else mention I ride before I say any more. 