I'm sure most people know about them, but if you don't it's a good place to hit for all sorts of gaming needs. Play N Trade is a national change and it's only local location is in the Walpole Mall off Route 1. Good amount of "classic" commons for the 2600 and Intellivision from $2-$5 each. A little on the high side, but you can find some good deals and fill in some holes in your collection. They also have a handful of Odyssey, TI/99 and other older items.
For the NES, Genesis, SNES generation, they have items from 99 cents and up. If you're looking for older sports game, most of them are 99 cents to about 3 or 4 bucks. They have a decent selection for all 3 systems (a lot for Genesis, including 32x and CD) and if you hunt for the cheap games definitely worth a trip. I was down there yesterday and spent 13.60 (after tax) for 3 Genesis games (Sonic, Super Monaco II and Virtua Racing) and 2 N64 games (Mickey's Speedway and In the Zone '98). Compared to E-Bay shipping fees, a much better deal than I'd get there!
BU
Also, if anyone has a Genesis 32x or Genesis CD they're trying to get rid of for cheap (cheap being the opportune word), send me a PM!