I just saw an ad for box.com and visited their site and watched their video. They appear to be most similar to dropbox with some resemblance to sendbigfile / kicksend and also some functionality of Google Docs. From their homepage (without watching the video) I had a hard time understanding what they did. They have a cloud based service and a fairly simple API that you can use to connect with it. It seems interesting but I’m not sure it will gain enough support to be around in the long run. Hopefully they will – competition is good.