Yeah the BS3 is the only system I know of that supports Racepak (if you buy their "Racepak" model) but not AiM - in every other way, AiM is more versatile/robust, whereas Racepak stuff works great as long as you have Racepak everything.
As far as the other dashes out there, we've used Pi/Pectel stuff with good success (with Pectel ECU), as well as the Motec SDL and ADL, which are amazing, but just stupid expensive.
For any of you guys that kart, the MyChron setups are right about $400 and come with senders.