The first thing you will want to decide is whether you are going with a regular television or a projector. They both have their pros and cons. A regular television works much better in bright rooms, like on the south side of your house.
The receiver is the key component in a home theater system, whether you're buying it separately or as part of a home theater in a box. Look for high wattage, multiple HDMI ports and preset sound fields that reduce echo for the most flexibility.