Hi pantscorcher,
Congratulations on the your purchase of the best biking gps IMHO

. you will definately need a memory card, I`d recommend a 256mb card which is sufficient for UK and trips to euroland unless you plan on very long tours around Europe, then you`ll need a 512 card. The base map sucks, i cant believe garmin have the gaull to still use this mapping, accuracy is off buy about 500m

So get city navigator V8 auto kit, which includes a memory card, CN V8 mapping which covers the whole of Europe, car mount and power cable with speaker (there are 2 differrent kits, 256mb or 128mb). There is a vast amount of adjustment for routing and settings with this unit, and depending on what settings you have, makes a big difference to the route the unit chooses, so take the time to learn how it works and you`ll be well pleased with your purchase. You can use the mount you get with the unit for use on the bike (unscrew the silver screw in the centre and then use the 4 holes to mount to the bike bracket), all you`ll need is a bracket to mount to the bike, I`m going to use the bm one.
I am in the fortunate position of being able to share the costs with my brother, so we got one auto kit 256mb for £205 (1 unlock code each), from Yachting Universe (do a search on the web), 1 x 256mb card from ebay for £68, 1 x garmin Topo UK for £120 from Wiggle bikes with 2 unlock codes (special feb price) and memorymap UK (the whole country), for £170 from cotswolds outdoor.
I wanted to be able to have a multi-purpose gps, bike, car and walking, so for about £750 I think I`ve got the best unit money can buy, infact I dont think theres anything else on the market that will do everything the 276c can, I`m very pleased with it.
By the way, you could just get Topo UK and a card, although if you were to just go down this road, I would recomend you go for a 512mb card as topo takes a fair amount of mb (alot more than C/N) and it doesn`t cover Europe. Topo will do routing and does give you POI`s and cities. I have England and Wales and the lower part of Scotland loaded from city navigator and a lot of the national parks from topo uk, loaded on a 256 card.
If you need any further help, do pm me and I`ll try to help further.