AquaFx, Coralife and Kent all make good systems.
I highly recommend you get a TDS counter as well, this will give you the Total Dissolved Solids in the RO/DI water, an indicator if you will that it is working correctly and when it gets time to replace the cartridges.
Another thing to consider is a Float valve as well to shut the system off in your water collection pale when it reaches fill level.
I just installed this system for someone and it is very very good.
AquaFX Mako RO/DI Unit - 100 GPD : Reverse Osmosis Units