Really, you don't need to worry so much about wattage. Some important things to remember when shopping for HT speakers:
1) Try to "timbre match" at least your front speakers and your center channel speaker. This simply means to stick with the same brand of speaker, and preferably the same model line. This generally ensures that the tweeter and woofers in the speakers are all made of the same material and oftentimes sizes. This will give you a smoother pan when you have sound moving across from one front speaker, across the center, to the other front speaker. Sometimes when the fronts and center are mismatched, the sound will change as the sound goes from one speaker to the next. It's not quite as important to timbre match your surrounds (but it never hurts), and the subwoofer is non-directional, so any brand will do. Do a search of AVS of subwoofer preferences and see what people like.
2) Make sure the subwoofer you get is a "powered" subwoofer. This just means that the sub has its own onboard amp, and simply gets the LFE (low frequency effect) signal from the receiver. The sub amp actually powers it, not the receiver. Most subs are powered nowadays.
3) The wattage of the speakers will most likely be all over the map, even if you stick with the same brand and/or model of speakers. That's really okay. Trust me. You're worrying WAY too much about the wattage.
My setup, for comparison, consists of an Onkyo TX-SR703 A/V receiver (100 x 7 watts/channel), Definitive Technology BP10b front speakers (20-300 watts/channel handling), a Definitive Technology CLR 2300 center channel speaker (20-250 watts/channel, with a built-in 8" sub with its own 150 watt amp), Definitive Technology BPX dipole surround speakers (15-350 watts/channel handling), and a Definitive Technology SuperCube II sub (powered by an onboard 1250 watt Class-D amp with an 8" long-throw driver coupled with two 8" pressure-driven radiators). As you can see, wattage is pretty much all over the map, but it sounds fantastic.
When you hook up your speakers, your receiver may have a built in equalizing system using a microphone that you plug into the receiver. This will pretty much balance out your speaker levels. If the receiver doesn't have this, learn how to use an SPL meter (Radio Shack has them) with test tones from the DVE or Avia calibration disc to set up the levels.
Even though I have Definitive Tech speakers (some people absolutely love them, including me, and some people hate them; that's why you need to go out and listen to different speakers to get an idea of how differently they sound), I really wouldn't recommend them for you. They're extremely sensitive to how they're placed in a room due to their bipolar configuration (identical drivers facing forward and backward), and take a lot more know-how to properly set them up. You could go with the Mythos line from Def Tech, which are your basic direct radiating speakers. Anyway, you could check out speakers from Def Tech, Klipsch, Polk, Magnepan, B&W, Paradigm, Martin Logan, NHT, JBL. etc (the list goes on and on and on). Browse through the speaker forum on this site to see what people have to say. Speakers can be very daunting to buy, because there are so many makes and models, people who love and hate certain models (and aren't afraid to say it), and price ranges. Best bet, settle on a price range, decide if you want a 5.1 system NOW vs. starting with 2 good front speakers and adding as you can afford to, etc. Really, worrying about wattage ratings is the absolute least of your worries.