Bork,
Garmin's top 2 handhelds would probably be the 76csx or the 60csx. Both do virtually the same thing (I believe the 76 is a bit more money) they just look totally different. I have a 76 and my buddy has the 60 (I'd take either one).
The "x" models have a card slot for expanding the memory capacity. You can just get a bigger card for them and load up more maps than you'll ever need. If you don't want to spend the money for an "x" model, you can get the 76cs or the 60cs. However at that point I'd get the 76cs because it has a memory capacity of 115megs and the 60cs has a capacity of 56megs.
The new Legend or Vista e-trex models also come in an "x" version and are very nice. The only thing I find with the e-trex models is, they can be very difficult to operate while wearing gloves. (small buttons).
Any of these would also work well in the car. But as I said before, you'll want to get "routable" software such as City Select or City Navigator. These have every street and address in the US and will give you turn by turn directions to anyplace you want or need to go. Topo, Roads & Rec and Metro Guide will not give turn by turn directions.
This is just my opinion, but the people that say they really like the Topo software, haven't spent the money on City Select or City Navigator. Once I had City Select, I've never used Topo Or R&R since. City Select or City Nav have tons of dirt roads and trails and forest
service roads on them.
One thing to keep in mind, all these handheld units work really well in the car (providing you have "routable" software) but all they do is give you a series of different sounding "beeps" when you need to do something. They will flash written directions up on the screen for you to follow. The automotive units on the other hand, will actually talk to you and flash written directions up on the screen. I ultimately ended up with one unit for the bike and another one for the car.
I'm not sure how much Topo is, but you can find City Select or City Nav for around $120 (buy it , it's worth it) otherwise, your GPS is just a big fancy compass. IMHO
Fell free to PM me if you have anymore questions.
Good Luck,
Keith