I also stuck with my MX-500's for a long time (i bought my first one from Circuit City the first day they got em in) but eventually moved on to newer URC models about 10 years ago. However the trusty old MX-500 is still the only universal remote my wife will use in her den and bedroom (she's rejected all my attempts to transition her to my R40, R50, MX-450, MX-780, & MX-890 units over the years).

If you liked the R50 form factor, the MX-450 is the "Pro" version of that unit with a few differences and is a solid Learning Remote. Good used ones are available on eBay for fairly cheap. They're pre-programmed but i didn't like the default layouts, so on mine i ended up creating my own screen icons where *I* wanted them, then just learned pretty much everything from my original remotes and created a bunch of activity macros. As learning Remotes go it was a good upgrade from the MX-500. There are several threads about it here in the Consumer Remotes and CCP forums.