Lang-8.com allows you to post a short piece that you wrote and natives will come correct it, for free. Since this pulls on the community, your posts are assigned a score based on how many "points" you have, which you earn by correcting others' enries. This really isn't as bad as it seems, since if you think about it, you are fluent in at least one language, so correcting others in that language is a piece of cake for you. Not only that, but you get to help people who really want to learn your language.
Some of my recommendations for using Lang-8:
For the same reason that you don't want to correct other people's massive essay-like posts, don't write something over three (reasonably sized) paragraphs. Not only does it make others more likely to correct your entry, but you also make it easier on yourself by having shorter posts. Since writing a short post is an achievable goal, you'll be less likely to push it off.
A good way to size your posts is to pick out five new vocabulary words that you have just learned. Write something that incorporates all those words. You will most likely end up with something that is just the right size. Also, when you come back to look at the corrections, you can focus on specific mistakes, in this case vocab usage, that can make it easier to learn from those mistakes.
Since life can get hectic, it may feel like a pain to correct others' entries so that your own posts can get enough points to get corrected. The secret here is to look for the posts to correct with the red writing that says something like "You get 2 times the normal amount of points." These are easy ways to quickly get the points you need.
I cannot stress enough how much easier it is to read colored corrections. You can quickly pinpoint where you made a mistake and best learn from it, so do the same for others. What goes around comes around. After all the goal is to help each other, so you might as well make the extra minimal effort to help out a fellow language-learner.