surround sound speakers, cerwin vega, sony, or polk audio?

Of the 3 I'd avoid Sony (and most Japanese speaker manufacturers .. although some Onkyo and Yamaha are good for the money). Canadian, US, British and Scandinavian brands are generally the best bets. Cerwin Vega had a good name, but Polk are more "today".

That said, I wouldn't put any of these at the top of my list. There are lot's of others including Klipsch, Distinctive Audio, Totem, Boston, Mirage, Infinity, PSB, Paradigm, ....

For a professional recommendation of top surround sound speakers see the link. That said, I'm not sure whare you are so you may wish to buy a locally supported brand.

Finally, 7.1 is nice, but I personally wouldn't limit myself to 7.1 speaker packages. It's just as good, cheaper, and less limiting to plan to add 2 inexpensive rear speakers to a good 5.1 setup.

Happy hunting.

I would stay away from Sony speakers. Sony isn't exactly known as an expert in speaker design. I would probably go with Polk Audio. Cerwin Vega is probably okay, but I have heard more positive reviews regarding Polk Audio and their speakers.