Windows 7 will be available on stores and installed on new systems on Oct 22 that is known as GA or General Availability.
RTM stands for Release to Manufacturing. It means that windows 7 has met a defined quality level and all the MS executives who have responsibility for Windows 7 sign off on the final code.
General Availability: 22 October 2009
Release to Manufacturing: End of July
According to Wzor Microsoft has already started working on SP1.
I believe most of the people would want Microsoft to concentrate completely on RTM and not on SP1, but it is also inevitable that service packs will appear at some point in the future.

