Any established web comic (having at least three months of regular, frequent posts) is eligible. Blogs, humor sites and the like are not.
Before you rush off, know that you will need to dedicate a little time to learning the site to make it pay off for you. I will be posting a tips essay here in a day or two. Also, you should have Google Analytics installed before you become active on the EntreCard site. You can join right now, and should if you're interested, because after the first 100 web comics join, no more 3000 bonus points. Just don't start throwing your points around until you have analytics and read the tips.
FYI, playing around on EntreCard increased traffic to Floating Lightbulb 800%, to my Scratchin Post comic 433% and to my other comic, Li'l Nyet, which was starting from a low base from being new, 8000%.
If you join, send me an email, and I will send you instructions to collect your 3000 points -- unless all 100 slots are taken by then. Include the name and URL of your comic!
I have no affiliation with EntreCard. I only know the owner because I suggested he try applying his system to web comics and he took to it. There are articles on the web about EntreCard, pro and con, but most of the ones I've read are naive in major ways, so it's hard to offer you any assurance of results or anything. But, it's free, and I tried it before I agreed to do this, and while it's not for everyone it can be helpful or very helpful for some.
My email address is in the right hand column. Finding it is your first test.
If you try it and it works out for you, the best thank you is to link to my sites. Thanks.