If you are going for Free ISP, I'd suggest having at least 2 ISP's because they are quite sketchy. Also, I would advise against using the Free ISP as an e-mail provider, unless it's webbased.
Important to note that the 2 ISP's should be on different networks.
The two major co-branding networks are: 1stup.com & Spinway.com. Spinway does Bluelight, Collegeclub, NBCi, and others - all the same network. 1stup does Altavista, Lycos, etc.
So I'd go to spinway.com - choose one (I recommend just getting the bluelight.com CD from K-mart. No banner ads on Yahoo sites, which is better than nothing).
Then go to 1stup.com and get one (I use Altavista because I like altavista search and it's in the banner ad)
You can also choose NetZero but I really think they suck and are very slow and unreliable.
Also, if you do go with a pay ISP. I'd recommend going with Costco/MSN. My dad has it and it's $11/month and they have a very reliable network. It has been down once, and I just used Altavista for that brief time.