Conduct Online Research
Having your website set up is just the first step, but you wont' get traffic, if you're not promoting it. Start printing your website on all public communications (literature, press releases, chum, etc.) and mentioning it when you're door knocking or doing call time.
Reach out to local bloggers. LeftyBlogs is a good directory of progressive blogs in all 50 states. DailyKos is a collaborative bloggers, with contributors posting diaries about everything imaginable. Reach out to these bloggers.
Just like with traditional media sources, you have to build relationships with bloggers. You can start by adding friendly bloggers to your press list and inviting them to cover campaign events.
Meet people where they are.
Most states have an email list-serv of liberal bloggers that you can get
access to. These aren't publicized, and
you will have to be invited. This is
where reaching out to the bloggers you've identified comes in. You can also buy ad space on relevant blogs
in your area, typically for an affordable price. 
Ask your new blogger contacts for their rates, which are usually a weekly flat fee. Be sure to tailor your ad to the audience of the blog. Buying ads on blogs engenders good feelings, and will make positive coverage of your campaign by the blogger that much more likely.
Advertise online smartly. Online advertising can take the form of banner ads, blog ads, and search engine ads, each with its own list of positive and negatives. The one thing to remember is that, if you're going to advertise online, it shouldn't be an afterthought.
Develop your ads with a specific purpose (e.g. list-building, volunteer recruitment, fundraising, etc.) and make sure the landing page matches that intention. If someone does click on your ad, you have a matter of seconds to convince them to take the requested action. Don't clutter the landing page-make the call to action as clear as possible.
If you want to learn more, here's a good study about the online ads during the 2008 presidential primaries.