TrixBrix has just launched a tremendous series of narrow gauge tracks. Narrow Gauge tracks for the LEGO train system are two studs narrower than standard gauge tracks. This means, that narrow gauge sleepers are just 6 studs wide (instead of 8 for standard gauge tracks).
Curves are available in three different radii (R24, R36 and R48), straights come in different lengths (2, 4, 8 and 16 studs). Switches and crossings are also available.
A very cool feature is that the narrow gauge tracks can be combined with standard gauge tracks. This means, that you can enhance a standard gauge track by some rails and make it available for narrow gauge trains. Check out the following example:
Luckily, the TrixBrix guys send me description and images of the parts in advance, so I was able to integrate the parts in the TrixBrix Track Library for Bluebrick on time.
I recommend to try out the narrow gauge tracks with Bluebrick first, then buy the tracks on the TrixBrix online shop at trixbrix.eu.
Update for the library is available here.