What do you have currently?
I did tons of reasearch before buying mine. I settled on the Yamaha MSP5 - very natrual sound, crisp highs and true mids but they are lacking in the bass but I'm planning on adding a sub later on. Didn't get anything bigger then a 5" because I had a tighter budget.
Rockits seriously knock loud, if you like bass go for them. They also look amazing which is always a plus
The Mackies are very popular in mainstream studios. They sound natural and have a much more flat response compared to the Rockits. I've heard they are good for dnb and electronic music production...though don't count me on it.
If you want something fun, Yamaha have the HS80m which are supposed to have the same signature sound as the NS10s. The H80s are good as an A/B set of speakers to check your mix on but they are still good at producing a decent mix.
Also check out the Blue Sky Media Desk 2.1. They are supposed be awesome.
Make sure you listen each set of speakers before you commit, which is where I went wrong with the MSP5's. Don't get me wrong, they are a good pair of speakers, but they lack bass which is what I really need.