Online Bookkeeping with Outright.com
Outright.com offers free online bookkeeping for self-employed folks and small businesses. It's very basic, but seems to have everything you need. I always wonder how sites like that are going to make money if the service is free and expect them to start charging once you got hooked on the service.
Anyway, they also have some good information on their site. See here for a post on quarterly estimated tax payments.