If you've got an Edge 800 you'll know that the basemap is useless, and that the official Ordnance Survey Discoverer map is OK, but expensive and cluttered when zoomed in.
TalkyToaster did some good work taking OpenStreetMap data and presenting it in the Ordnance Survey style. I've done something similar, except I've tried to make it a bit clearer (wider tracks and roads, brighter colours etc), and more importantly, I'm not charging for it.
This is my first foray into Garmin mapping so I'll try to update this image as I get more familiar with the map creation tools. The map below is based on the most up-to-data OSM data.
Huge thanks to Nick Pinn for starting me off with his OS-style type file and providing helpful support by email.
Download link and installation guide below the screenshots.
Copy directly to your Edge 800's memory card. I see no reason why this shouldn't work on the 810 or Touring.
Enable the map:
Go to Settings -> System -> Maps and make sure it's enabled. You might want to adjust the detail level as it can get a bit cluttered on levels above "Medium". I'm aiming to fix that it in the next release.
OpenStreetMap data is good but is missing the odd path. It's also not verified and subject to error. Relying on this as a sole navigation source is foolish at best and reckless at worst. That being said, I've not encountered a problem.