Online IM site that includes file transfers?

I’m looking for an online IM site, similar to meebo, that also allows file transfering from MSN/Yahoo users. Ideally I can log in to multiple MSN and Yahoo accounts. This would be file transfers directly from ‘IM site’ -> MSN/Yahoo, NOT ‘IM site’ -> ‘IM site’. A list of sites would be great incase my corporate firewall blocks some of them. Thanks!