On Helium, Associated Content, Etc.
Online sites like these, which seem to launch and die every day, use the desperation of aspiring writers wanting to see their stuff published as a way to load up content virtually free of charge. Sounds like a great deal---for THEM. But if you understand that going in, fine. Just use them back, by getting some exposure on the net and developing a voice and getting into the habit of writing regularly. Just don't get addicted to the experience, because it'll likely never lead to much and will make you lazy as a writer (since there's no editor supplying a critical eye and ideas for revision). You're better off trying to write for small papers and magazines in your hometown, or contributing small things for more respected online sites, then continuing to work your way up the Helium, Associated Content, etc. food chain. Of course, the process of having rejection and the annoying suggestions of editors in the mix will make it harder, but at least it has a chance of helping you eventually become a professional writer.