For a year or more (though not lately, I must confess) I've played bridge online at Bridge Base Online, which is really great, but requires Windows-only software, thus excluding many lovely people of my acquaintance, or making them jump through emulation hoops.
Until now -- BBOFlash, a beta version of which is available here, runs in a browser window on any computer you happen to have. On Macs, it seems to work least crashily using Explorer.
Check it out, people! I'll see you online.