Cowboy Bebop - everything, and this is hands down the best anime soundtrack of all time. It's so extremely diverse, and it never comes up short.
FLCL - everything
Escaflowne - anything with chorus/orchestra

"Free Bird" from Haibane Renmei
That piano song from Big O that Dorothy always plays. Plus the ending theme.

And, how could we ever forget
LUPIN THE THIIIIIIIIIIIIIIIIIIIIIRD
I love the main theme to that show. Which is cool, because comedy anime generally have crappy music, unfortunately.