For cheap add-ons, I'd recommend getting a pair of inexpensive small speakers to use for rear surround sound. When I first got a Pro-Logic receiver, I went and got a pair of speakers from Radio Shack for $20. The speakers just had a single small cone in them and weren't full range, but you don't need that for Pro-Logic, and just the addition of sound coming from the rear was a great addition. Next you could get a cheap center channel speaker, but it's best to have the center and front two speakers be similar because you want the sound to be similar as it passes from one to another (say, as a motorcycle goes across the screen, you don't want it to to sound like a Harley in your left speaker, sound like a moped in your center, and then sound like a Harley again in your right speaker). It's not nearly as important to have the rear speakers match the fronts.