With Roberta's Blood Trail expect to be thinking and/or saying "Holy ****ing shit! O___O;" a whole lot.
Gintama is on this list for a single fight! It's that awesome. The fight where Kagura snaps is amazing not only in action but also in it's ability to send a chill up my spine every time I watch it.
If I have to explain why GANTZ is on this list then it's because you haven't seen it yet. I suggest you do so now. Though prepare for a pretty pathetic end to the series. Just a fair warning.
Read or Die TV may not be the best anime out there but it has some really good fights in it with very diverse and fluid movement.
If you don't understand why Samurai Champloo is on this list I suggest you go find out for yourself, you'll be glad you did.
Same goes for Trigun and both FMA series.