I've got two of the green fake-grass battlemats by citadel / games workshop, and I decided to try adding some detail to one of them today, being bored of a flat green featureless battlefield. So I got some browns and some greens and painted english/french style fields onto the mat, but only lightly so that it can still roll up and unroll and still maintain the colouring.
Anyway, for full details, see my 15mm historical blog at: http://pauls15mm.blogspot.com/
It's a bit rough, but I like it. Here's a pic with some sci-fi terrain and some mechs on it!