The ReefKeeper 2 is kind of outdated at this point.
Personally, I think probably the best bang for your buck is going to be either the AquaController 3 (around $450 I think) or the ReefKeeper Elite (around $490) with maybe a slight advantage to the RK Elite.
These controllers can do multiple tanks, have some cool and useful add ons (moon lights, Tunze controllers, etc.), and are reasonably priced.
If you're interested in all out features and modules, Profilux and Aquatronica seem to be some on the top. They have Koralia controllers, Tunze controllers, dosing pumps, internet options, SMS options (will send you a text if your power goes out), light dimmer options, etc. However, they're European companies and are expensive. I run an Aquatronica, but the only reason is because I got it for a really good deal from another guy in the club.

I do love it, though, and support on the unit has been fantastic, even though the parent company is in Italy. In fact, I've got a brand new system I just upgraded to coming to me some time this week, and I'm pumped!
But anyway, check out
www.aquariumcontrollers.com. There is an awesome Excel spreadsheet there that shows all known controllers (except maybe the ReefKeeper Lite, which I think may have the same feature set as the RK2) that you can actually checkbox and compare controller features side by side.
Hope this helps!
Brandon