Totally going to second the rec for Trigun. Until FMA, for about 4 years straight, Trigun was my absolute favorite anime ever ever EVVVVEEEEEERRRRR.

Blue Seed is also entertaining in it's way. The first half of the series is pretty repetitive, but the second half escalates and escalates in some very cool ways, culminating in an intense finale. Not anywhere near Trigun intense, but still quite rockin'.