Besides the usually such as digg and squidoo.
Not the usual for everyone.
I suspect you're looking for places you can post that are guaranteed to accept your submission, or who have basically no standards or barriers to entry. Places like digg and squidoo. I don't have a lot to offer, other than if you're looking for a paid service, check out the exhibitors at pubcon: [pubcon.com
...] . One of them has a service somewhat similiar to what you're talking about. Kind of a pyramid of blogs and stuff, with squidoo and a few others at the top of the pyramid.
If you're looking for 'real' blogs, then you can find them in your niche by searching for them. Serious, successful bloggers have two problems - they want more content and are happy to have someone else write it for them, and secondly, it's an overwhelming amount of work for them to sift through the proposals for guest articles they get. So getting their ear can be difficult.
For those folks, I would approach them by suggesting that if they'll consider a guest article, that you will pre-write an informative, non-promotional guest article. You'll give them three subjects they can choose from for the post, and you'll then write the article - under no obligation to them. They don't have to agree to publish the article until after they've read it.
You might even try sending an example article along with the request, so they can see how you write.
This only works though if you write articles of high enough quality that a top blogger would publish it. But this technique definitely takes the pressure off the blogger of having to sort through whether you're a decent writer or not - and that is a big concern for them.