We're using Dropbox but in order to share files >2gb, each sharer must have premium Dropbox account. I resent this pricing model as it is unfair and am resolved to finding a more open solution.
This is one of the best guides I've found on the topic. dropbox clone how to
SparkleShare looks like they want to be the FOSS equivalent to dropbox, with clients for linux, Windows, and OS X. Unfortunately, it looks like they're still in the early stages and only have betas for linux and OS X; no Windows.