GPS
I have a Garmin GPS V and my next will be a Garmin 2610.
The GPS V and other small units have a limited memory, so the reason for multiple data sources like CDs is to load the GPS with the information in the area you will be using it.
For instance, The Garmin GPS V has 19 megs of storage. It has the United States down to the local highway level, but does not have back roads nor some fairly major local highways.
I use the GARMIN MapSource Roads & Recreation disk because it is a good source of back roads. There are others as well. The GPS V is very rugged and very high resolution screen. You can get extra power cables and have one in each vehicle. The internal batteries are a real pain. Just take them out and use only vehicle power to run the GPS. Make sure the power is hot all the time and fused with 2 amp inline fuse. that way, you don't have to reboot each time the engine is shut down. I believe the GPS V is the best bet for the budget minded because it is weather proof for the bike use. MY GPS V survived a 75 mph crash that totaled the bike. I still use it. It was used for 90,000 miles on the 01 wing, 23,000 on my old 93 Wing after the crash, and 11,000 on my 04 Wing. It is never turned off. I just turn the backlight illumination off when I put the bike to bed.
If you are going to spend more than enough for the GPS V, don't stop until you have the Garmin 2610. You will end up with one anyway, so dispense with the inbetween steps and go for it.
The 2610 has a large colored screen, a big plus. It uses the removable Flash Card for memory and that is the biggest plus of all. That is cheap memory and available everywhere. You can get the Flash Card now at one Gigabyte, that is 500 times as much memory as the GPS V.
http://www.memorysuppliers.com/ibmmic1gbwtr.html
What's more, you can have several of them if only a gig is not enough.
It is really frustrating to be enjoying a great new back country road on a trip only to run out of the area that you down loaded before you left.
It will not take you long to become addicted to the GPS if you get a good one. Most serious tourning riders will agree that a GPS receiver it is the greatest single accessory you can put on a touing bike.
Getting caught out in a rain storm with only a paper map to find your way is hazardous while just following the instructions on your GPS works in all weather.
OK, I am addicted. It is habit forming. I can hardly go the the bathroom without a GPS.