Switching ISPs wireless router advice?

When it comes to networking, I'm pretty much as clueless as the average PC user. So soon my family is going to switch our home internet from a 3 meg AT&T line to a 12 meg from Comcast, for the same monthly price. We're also going to get a new wireless router/modem because our is toast, it's really slow and drops all the time. WoW doesn't even work anymore except on the one desktop that's wired.

So, when we get a new router should we just buy whatever one from Comcast, or should we tell them we're just going to get our own? What would be a good router for us? The one from Comcast is $75 so we could probably spend up to $100 on a decent one. Also, right now we have a router and modem in one, it plugs directly into the wall with a phone line. I don't have a modem and I'm not sure how many aftermarket two in one deals like that are out there. Like I said I don't know much when it comes to networking