Today I rode on 487 from Jarrell (25 min N of Austin) to Devilla, then to a cool little hole in the wall called "pancho's and lefty's" in Hare (middle of effin' nowhere). Then to Circleville, left on Hwy 95, through Taylor and back towards Round Rock. Awesome ride, scenic.

 

I'd have to throw in the Willow City Loop if you're in the Fredericksburg area. It's a short ride off off Rt 16. Depending upon the time of year, there might be one or two water crossings and it's likely you'll come across a few free range longhorns.

Also, there's a publication called Ride Texas that's well worth getting. They also publish a pretty decent Texas ride guide that you can actually get at a lot of bike shops.