I've been thinking of buying a receiver, and want to connect my laptop/ipod. Can you just get a cable that has a USB on one end and an Audio input on another? What criteria would you use to assess amp/receivers?
Regarding hooking up audio devices to a receiver, the cheapest/easiest way I know how is with a RCA to 3.5mm cable such as this
http://www.monoprice.com/Product?c_id=102&cp_id=10218&cs_id=1021804&p_id=665&seq=1&format=2. You just plug it in to your headphone jack - works with cell phones, iPods, tablets, even laptops and desktop computers.
Regarding the receiver, they run anywhere from $100 to $2000+ brand new. A lot depends on if you plan to have multiple audio sources and if you plan to hook it up to a television. At its most base level, you can use an amplifier like FastEddie911 posted where it receives the signal via the white/red cables and outputs it to 2 speakers. There are other options like iPod docks or bluetooth connections but those come at a price.
Spend a little more and you can have it output to 2 speakers and a subwoofer (or 2), or 5 speakers or 7 speakers. Some have a 2nd zone so you can run wire to speakers in your kitchen or on your patio and play it in a 2nd listening zone. From a purely practical standpoint though, you'll want to look for the output rating of watts and at what ohms to match up to your speakers. Is it worth an extra $200 to go from 90watts per channel to 110 watts? Not to me, not for what I use it for.
From my experience, Onkyo, Denon, Harmon Kardon, Pioneer, Yamaha all make good receivers.
This can all get expensive in a hurry which is why I prefer buying 2nd hand. Not to mention, most speakers require a break-in period which means somebody else using them has already done that for me :)
side note: Monoprice has very good price for speaker wire as well. I prefer a 14 or 16 gauge for my distances - you could get away with 18 gauge for shorter distances in my opinion.