As mentioned, your speakers will dictate the capabilities of the receiver/ amp . 8ohm speakers with good sensitivity are easy to drive and any receiver will be able to handle them. 4ohm speakers with lesser sensitivity will be tougher to drive and will require a higher end receiver or a dedicated amp.
Your budget should be divided as follows,
50-60% Acoustics (Speakers, Subwoofer, Room Treatments, etc.)
50-40% Electronics (Receiver/amp, CD/DVD/HD-DVD/DB Players, Display/ PJ, etc.)
Regarding receiver/ seperates, one option is to get a mid range receiver ($750-1000) and a 2 channel amp for the Mains (or 3 channel amp for the Mains and Center).