I'm not sure how wireless you want them. Pretty much every option I know will still require a power cord and speaker wire to the speaker. There are a few decent options for eliminating the run from the front to the back of the room.
The Kef wireless system is good and you can put the RF Receiver/AMP right at each of the surround speakers, however you pay the price at $600.
[Link: kef.com]The least expensive solution that I have used for many random applications, such as back ground Zone 2 music in another room, or surrounds speakers, is the Bose SL2. This is a non proprietary piece. Its basically a Transmitter that you feed your SL & SR signal into (stereo 3.5 connector) and a Receiver that has the amp built in and speaker level outputs for SL and SR speakers.
[Link: vanns.com]At only $249 this is a decent solution. HOWEVER, in both of these scenarios, you have to have an AVR with Preouts. These options also allow you to use whatever speakers you want.
I have no idea how good this is, but you could do something like this:
[Link: thehomeautomationstore.com]And just use your own 2 channel amp, but again, need an AVR with preouts.
I'm sure there are many basic stereo wireless send/receive gadgets out there.