I checked the Surly web page for their Steamroller. It's chromoly and they listed a 120mm rear OLD.

So what's your budget and what's this about "light touring"? Do you have front and/or rear brakes already?

The most straight forward option would be to get a new Sturmey-Archer SRF3 hub and build it into a wheel with a rim that matches your front (easy build - no dish). For the aftermarket this widely available, beautifully polished alloy hub comes complete with a twist shifter and cable and a hub-attaching bracket for terminating the cable, so you in fact would only need to zip tie the cable housing to the downtube/chainstay. Your OLD will be fine with the SRF3.

If you have drop bars you can use either a classic Sturmey trigger positioned in any convenient place or a LH triple brifter to accomplish the indexed shift.

The SFR3, like it's 70 year old parent AW3, offers a 177% gear spread. If that's not enough for your "light touring" duties, then there is the Sturmey SRF5 with a 225% gear spread or the SRAM Spectro P5 with a 251% gear spread. For flat bars, you have a choice of a twist, trigger or a "Rapidfire" style shifter for the Sturmey, but only a twist shifter seems to have real-world availability for the SRAM. For drop bars with either, you'll probably wind up with a twist shifter on a Hubbub adapter.

If "light touring" is more involved, and because the Steamroller is a steel frame, you can reset the rear OLD and use either a Shimano Alfine 8 or SRAM S7 or iMotion 9-speed hub. The Shimano offers a 306% gear spread, the SRAM S7 303% and the SRAM a 340%. Neither the Alfine or i9 is cheap compared to a three-speed hub, or expensive compared to a completed derailleur set-up.

One last thing: if you'd like to stay fixie, Sturmey Archer is coming out with a three speed fixed gear hub in early 2009. This S3X hub will have a 160% gear spread and will use a barcon shifter.

So, mull this over, google around, and feel free to come back with specific questions.

HTH,
tcs