Let's see...
-Gundam 8th MS Team: Probably one of the few well-written and dramatic Gundam series to date. It's a much darker and more realistic take on the 0079 war. See also 0080:War in the Pocket.
-Gensomaden Saiyuki: A well-written spinoff of an old folk legend. Features an awesome plot involving demons, the reawakening of an ancient evil, and a dragon that can turn into a Jeep. What's not to love?
-Monster: This is my personal favorite anime of all time. Incredibly dark and amazingly deep in terms of plot. A veritable roller-coaster of well-thought-out twists. Very slow-paced, however.
-Spiral: A nice little detective-esque show. I whole-heartily recommend it.
-Prince of Tennis: Yes, a sports anime. It's incredibly well-done for one, almost no character seems thin and static, and there's enough physics-defying awesomeness to make Dragonball Z's jaw drop.
-Witch Hunter Robin: Watch it.
-Wolf's Rain: Once again: Just watch it.
I'd also recommend Trigun, Samurai Champloo, Stand Alone Complex, and Cowboy Bebop, but it seems you've already watched them.
Another thing: Be sure to watch the preceding with subs, not english dubbed. I assure you the dubbing is horrible on each and every one.