Today Microsoft has made available Windows 7 RC to partners with MSDN or TechNet subscriptions. According to the Microsoft Partner site everyone else will be able to download Windows 7 RC starting on May 5th.
Update: It looks like someone at Microsoft may have jumped the announcement a bit. The download link is now gone from the partner site and so far only the beta are showing on TechNet and MSDN. I am sure we will be getting more news on this soon.
Update 2: The RC will be available to the public on May 5th but TechNet and MSDN subscribers will have access on April 30th.