Tim,
I have a JHP-520 handheld nav/com. I think it is the cat's meow. However, there are a lot of newer ones out there now that are considerably smaller that may be comparable price wise, but are easier to keep in a flight bag.
If I may share a couple of ideas on accessories...
I have a lapel mic that plugs into the top of the radio and the mic clips on my shirt just under my ear. I use one like that on my radio as a Paramedic, and when I'm walking around at a fly-in or airshow, I can hear everything that comes across while leaving the radio clipped to my belt.
I also have an adapter that will allow me to plug my headset into the radio. An additional feature of the adapter is that it has provisions for a separate push-to-talk switch. The PTT that I have also plugs into the adapter and, when it's velcro-strapped to the yoke, works just like the installed radio. That setup saved my butt on my trip from California to Texas with Silverlining, as well as on my trip up to Clinton last month when my voltage regulator took a ciesta.
The last item that is very nice to have is an alkaline battery pack. That let's you use the radio at a moment's notice regardless of the health of your Ni-Cad battery pack. Invariably, you'll find yourself wanting to use the radio and the batteries will be dead.
I can think of no other more useful backup equipment for your plane than a handheld radio. Sometimes, the handheld GPS is used for backup, but it's my primary means of navigation now. I'm really spoiled.
