The Logitech/Harmony staff told me during a support call that all of their remotes use the same firmware engine. So any Harmony will work, although you may need to 'learn' IR codes for the latest/greatest devices.
I've got a 659, 688, and 880. The 880 is really nice b/c the menu/exit/guide/info buttons are larger, and it's got built-in rechargeable batteries. It costs a bit more, but deals can be had. Do your homework and buy one on the web. Retail prices don't generally stray from the bloated MSRP.
My wife ordered a Toshiba A2 for my christmas gift, I expect to use the 880 with it.
