How did I not notice this thread before? I'd hate to leave it at only one, since there are so many anime out there that I've loved watching over the years, so here is a list of my favorites, in no particular order:
-Ranma 1/2 (That one kind of goes without saying doesn't it?)
-Night On The Galactic Railroad (Watching this movie is an experience in and of itself.)
-FLCL (Because I love the pillows.

)
-Death Note (Once you start watching this show, you pretty much have to keep watching until it's over, with the occasional breaks to eat and sleep.)
-Mushishi (Just an incredibly beautiful show. It's kind of sad it isn't more popular.)
-Spirited Away (My all time favorite Studio Ghibli film.)
-The Twelve Kingdoms (So amazingly good, but it leaves you with many unanswered questions. I still haven't read the original light novels that continue past where the anime ends.)
-Trigun (Vash is one of the only male characters I ever strongly identified with, because he's always try to do the right thing, but ends up with everyone hating him just for who he is.)
-Azumanga Daioh (You laugh the entire time you watch this show, but then you cry when it ends.

)
-Neon Genesis Evangelion (I have no idea what I just watched. 0_0)
-Excel Saga (I still have no idea what I just watched. 0_0)
-Kino's Journey: The Beautiful World (Another incredible anime that is criminally under-appreciated. It has some sort of transgender themes too, which maybe the guys here could relate to?)
-Fullmetal Alchemist (It was really fun watching this with my brother.)