I'm not as knowledgeable as most around here, but I can tell you that you will want a A/V receiver as opposed to a stand-alone amplifier. It will tie in all your game systems into one unit where you can just switch the picture and audio with the push of a button, and it will power your speakers also. What receiver you will want will depend on the features you desire and the kind of speakers you intend to get. If you want power hungry speakers you will need a receiver with more watts per channel. If you watch blu-ray discs, you have to get an AVR that will accommodate that type of signal, and so on.
Accessories4less.com has very good deals on receivers, as does Amazon.
Personally, if I were in your position, I would spend about 350 to 400 on a receiver, and the rest on a decent pair of Left and Right front speakers, and then save money later on to build up your system a piece at a time (in the order of a subwoofer, center channel speaker, and then surrounds). But if you are in a hurry to get a home theater right away, there maybe some acceptable HTIB (Home Theater In a Box) wherein you buy the whole system in one package.
The reason why I would just buy a receiver for now and only two front speakers is because, for me, two (or even one) good speakers sound a lot better than a whole bunch of so-so ones. And, on top of that, selecting and shopping for the different parts of the rest of your system is fun (especially the subwoofer part). And seriously,the subwoofer in any HTIB is bound to be lacking, especially once you hear superior systems.
Some inexpensive speaker suggestions for the fronts I would give are the Infinity Primus p362 tower speakers, or, if you don't have room for towers, the HSU HB-1 mk2 bookshelf speakers. Either would be ideal, as they sound fantastic and are very power efficient so even inexpensive receivers can drive them well. A quick search on ebay brings up a buy-it-now deal on a pair of p362s for only $207 with free shipping, which is a outstanding deal! The HSU speakers are available from hsuresearch.com for $150 a piece, and $30 for shipping. I have both which is why I can recommend them, and a pair of either one will blow away any equivalently priced HTIBs.
But there are a lot of great speakers out there that will fit your budget, those are just the ones I personally know about, and I am sure you will get lots of great suggestions here. And whatever you decide on, come back here to get suggestions on how to set it up, because a improperly configured system is a lot of money wasted, and you have a vast amount of free knowledge at your disposal here.
