One thing to consider is the speaker's frequency range.

I have a friend who got the aforementioned Presonus kit, but has yet to get the computer to hook it all up to, so I look forward to hearing it but can't comment yet.
I did note these speakers only go down to 80Hz ..

The ones mentioned by VideoTrack and Don go down to 50Hz, which is a little better but still not quite what I personally need for monitors.

In my research you need a little bigger woofer to get down farther in the lower range.
However these take up more room, so there is always a tradeoff.

I do not work here, but the benefits are still awesome
Make your sound your own!