I use Soundcloud for posting audio only tracks. Uploading is straightforward and you can send people links. One great advantage is you are not limited to mp3 as their criterion is playing time. The free version gives you 2hrs playing time and the files can be any format include wav. I used it to send in my tracks for the Mudcat CD.

Quite a few people use dropbox for sharing files. I don't know much about it as I have not used it myself, but it seems to be another option.