I have a bike set up with a Sturmey Archer AW, 39/17, which has a nice gear range. Tops out at around 6.3 gear ratio (see Sheldon), with a a low gear low enough to climb most hills comfortably. The problem is finding a rim with 40 holes, if you want to build a new wheel. And if you're doing anything other than "light" touring, you'd probably want more.