Replaced by http://www.thingiverse.com/thing:627447 which has the entire band.

The band on my Pebble split, so I printed a replacement.
Included is the STL file, which matches the Pebble band, and the OpenSCAD source file in case anyone wants to tweak it.
Note that I only modeled the strap that broke. I kinda like the contrast between the black and yellow so I didn't print a replacement for the other strap. The strap that broke is the more likely one to break for others, so hopefully it's still useful. Or it'll inspire someone do do a few more lines of OpenSCAD coding to model the other strap.

UPDATE: I added the rest of the band at http://www.thingiverse.com/thing:627447 .

Printed with NinjaFlex, with 100% infill, at 30 mm/s. Should work with any flexible filament (FileFlex, Taulman Nylon, etc.). I just happened to have some NinjaFlex that I wanted to try.
Remove the wrist band from the Pebble. Use a small screwdriver or knife blade to press the spring pin down and remove from the Pebble.
Slide the pin out of the Pebble's band, and slide it into the hole through the printed band, then put the pin back into the Pebble by pressing spring pin down, sliding it into the Pebble, and letting it snap back into place.
Revel in wearing your own printed watchband.