Audio!
Got a couple of long rides comming up in the summer on the beemer, plan to take it for some longer runs too, need to look into audio/sat nav options.
Simple way, get Zumo 660 (£400)
http://www.brighthub.com/electronics/gps/reviews/35188.aspxHave it mounted like this... (image big so linking)
http://i209.photobucket.com/albums/bb315/Yonkyo/P5050016.jpgHas SD slot, so can chuck tunes on that, allows custom route planning to pick the nice roads, can be paired to my phone, has mic and headphone jacks so easy to plug in. I have a company phone which has unlimited bills, so to talk to people on the go, i can just call them....
Power wise can just get the aux socket installed next to the screen on the bike.
Other option, and more proffesional route. Is Autocom...
http://www.autocom.co.uk/Systems/Basic kit not cheap, £300 for that, then need to buy a VOX radio, i could plug my PDA into that for TomTom (use Tyre for custom route planning) then get a cheapo mp3 player or use the PDA for both. Would need to get some kind of ciggy adaptor to run muliple plugs, as my bluetooth GPS would need charging too, also have to get a tank bag to put it all in.

I am swining more to the Zumo as it will just be plug and play :-/