While City Navigator is a great purchase for POI information especially if you are going to use the GPS in both car and on bike, you can get tons of free maps online via a simple Yahoo/Google search. The maps for North America are at least as detailed as those Garmin makes available for purchase. The other cost of purchased-from-Garmin maps is that they are now "locking" maps to specific GPS units - yep, you have to repurchase the maps if/when you upgrade to another unit or replace a damaged one.

I also recommend the use of eneloop rechargeable batteries. They seem to last longer than any other batteries out there.

Thanks for the link to the REI/Garmin Oregon 450 - might go buy that myself later today.