I've recently bought a cheap second-hand GPS and have been playing about with it. One thing it's introduced me to, is Open Cycle Map, a sub-project within Open Street Map. The idea behind OSM is to generate open-source map-data, which people can use without the usual restrictions that apply to data from Ordnance Survey (see this for the whole story). The Open Cycle Map project plans to use this data, to plot the National Cycle Network, along with other useful cycling features (shops, cycle parking, etc).
The map already seems considerably more user-friendly than that on the Sustrans site and will presumably only get better. I've already started contributing to OSM (tagging up some pubs in my local area, natch) and hopefully once I get a bit more up-to-speed with my GPS, I can start adding some cycle routes too.