I use http://ge.tt for this. No sign up needed, no upload size limit, and better yet - the other person can start downloading the file as soon as you start uploading. How is Dropr better?
View Dropr.in not as a replacement for Box or Ge.tt, but as something completely different. Ge.tt is about as close as it comes, but they're viewing your data as a cache of files with free accounts limited to 250MB of storage. We're not a "cloud storage" provider. We let you quickly transfer files between devices without having to jump through any hoops.
This service is very different from Dropr.in. We're not trying to be "Bittorrent in a browser". Our goals are simplicity and convenience. Looks like a nice site if P2P is your need, though.