Pioneer Elite, Denon, and Harman Kardon are three good brands. They manufacture mainstream, high powered, and feature packed A/V digital receivers for use in home theatre surround sound systems.
Your first decision should be if you wan 5.1 or 7.1 surround sound. 7.1 receivers utilize 3 front, 2 side, 2 back, and 1 subwoofer. 7.1 is the standard for movie theatre THX sound. The 5.1 system do away with the side speakers.
Some of the newer features include Dolby Prologic IIx decoding, which takes sound from sources in 5.1 and produces 7.1 sound. Another feature is video up converting to 1080p HD from a lower quality analog input. One additional advantage of running your video output through a AV receiver is that many have a sound leveling feature that keeps the sound level constant and prevents loud commercials.
If you have decent 8 ohm speakers than you want at least 100 watts per channel. Also look at the sound frequency, 20Hz-20kHz can produce a wide range of sound, Next make sure the THD level is low. The normal options for THD are 0.9%, 0.8%, and 0.5% distortion levels.
Digital receivers are iPhone / iPod capable if they have a USB input or Bluetooth feature. Get one with a from HDMI cable if you want to easily connect your laptop and output 1080p HD, although the back connections work as well and a receiver with good video up conversion in theory should work if you have an analog output.
Some AV receivers come with a microphone and have an automatic room calibration that tunes your speakers and adjusts settings custom to your specific room.
