Oh I should have mentioned that I've already got a clear map holder but I wanted something a bit smaller and neater than that.

The Givi I mentioned actually has a black top to it, and would neet modifying.

http://www.givi.it/prodotti/img/130_84_imgprinc.jpg

Ah right. Not sure how easy it would be to make a clear top for something like that. How about getting a proper weatherproof case and adapting it to strap to the bike? Might be easier.

http://www.sailgb.com/p/waterproof_pouch_pda/
http://www.memory-map.co.uk/acatalog...oof_cases.html

Picked up the TomTom GO duty free at the weekend... £260. Sorted.