Let's see.... long list time. This is just off the top of my head, and I'm assuming you've seen a lot of the "standard stuff," so to speak, so... yeah. Highest recomended titles in Bold.
Anime
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G Gundam - BADASS MECH FIGHTS
Turn A Gundam - Another Gundam, but pretty much the best. Very unique and cool.
GaoGaiGar - GOLDION CRUSHAAAAAAAAAAAAAAAAAAAAAAAAAAAAA!
Aria - Slice of Life, very good.
Gunbuster - If you've never seen it, go watch it. NOW. Short, but sweet.
Kaiji (and Akagi) - Awesome as hell moments. A little slow, but so suspenseful it kills.
Black Lagoon - An action trip that really delivers. Good characters, animation, etc.
Sketchbook - Another slice of life. Slower than most, but really cute.
Legend of the Galactic Heroes - Anime at it's finest, right here.
Code Geass - Controversial, but I think it's quite good, aside from certain Sunrise moments.
Hidamari Sketch - Again, slice of life, but one of the funniest I've ever seen. Also, nutbladder.
Gankutsuou - A masterpiece. Absolutely thrilling.
Mushishi - See above.
Kino's Journey - See above.
5cm/s - Movie made me cry like a little girl. Very touching, and visually stunning.
Toshokan Senshou - Currently airing, and one of the only good shows this season. Fun times and action to be had.
Hokuto no Ken - YOU'RE ALREADY DEAD.
Goldenboy - Funny as hell, and one of the best dubs ever.
Shigofumi - Short one, but quite good.
Manga
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GTO - Funniest manga ever. Read it. Love it.
Jojo's Bizarre Adventure - Manliest journey ever. Absolutely AWESOME.
Vinland Saga - Vikings.
Violinist of Hameln - Old school and funny as hell.
Yokohama Kaidashi Kikou - Amazingly relaxing, and incredibly good.
Blame! - Crazy stuff. Very good.
20th Century Boys, Monster, Pluto - All by the same author, and all brilliant. Must reads.
Parasyte - Weird, but good. Great action scenes.
Planetes - Great manga with great characters. And space.