There are lots of options that don't have the serious suck-factor of Trigun. Cause believe me when I say this, I agree. It's kind of a shitty show, bad plot, worse characters, and horrendous production values. Few redeeming factors.
I do believe Ghost in the Shell has shown up, and I'd agree it's definitely a good call, though it doesn't have the blend of mature (and by mature I mean mature, not "inappropriate immaturity") humor and serious thematic elements of Bebop. It's only got serious thematic elements, most of which are more political than they are emotionally or philosophically charged (like in Bebop. Still, it's a good show, with solid characters, an interesting well developed, if at times convoluted, plot, and some really good production values.
If you don't demand action, Mushishi would also be a really good call. It's more a blend of fantasy and slice of life. It's pretty quiet and contemplative. It's also one of the most original and by far one of the most beautiful animes around. Every time I try to describe it to someone I end up lacking for words to properly express even the most basic plot elements. It's kind of just one of those things you have to see to get, so try and watch a few episodes (you probably won't be able to get a feel for it until you've seen the first three or four) if it sounds interesting.
Ergo Proxy is good, though it does take itself just a little bit too seriously at times. It kind of threw me off at first, cause it wore the garb of a post-apocalyptic utopian narrative, which I'll be honest is a theme that has been so played to death that it's not even mildly interesting anymore. That said, once you watch it a little more you come to realize that that's just the backdrop for the real show. So it's another good one to look into.
And my last suggestion is going to be two shows, which even though remarkably different aesthetically, have a lot of similarities, probably due to the fact that they were both directed by the same person. Ghost Hound and Serial Experiments Lain are both weird cerebral forays into some of the nether-realms of science fiction, linking real world concepts, from psychology, quantum physics, etc, into the plots of their story. The end result is an oddly compelling completely unique series of plot points that you'll probably not be able to see coming before they hit you. And I can't suggest either highly enough.
