It depends what you want. How big is your site, how many visitors, what sort of traffic, how many e-mail addresses you need etc.
For a simple 50mb web space, 50 pop3 e-mail addresses, cgi support, I use your-site.com which costs me $5 per month.
Similar package on powweb.com but with 250mb space
basically, work out what you need first then work out who can provide it.