Salsa has partnered with Revelate Designs and I believe they really have a good thing going here. Frame bags for the Salsa Mukluk are already available and similar bags for the Fargo, El Mariachi, and Spearfish will available in early 2012.
Kudos to Salsa for getting this done. It's my understanding (Thanks to Joe) that Revelate is also making frame bags available for the Surly Pugsley and Moonlander. I had stated earlier that this wasn't the case. Salsa had this news posted on their blog, but Surly made no mention of it that I could see on their blog. Eric from Revelate Designs has posted on their blog that Pugsley bags will be readily available soon. My guess is that they will go very fast. Thanks Joe for correcting me on this.
I have several of the Revelate Design bags and they are definitely top of the line gear.