From the earliest days of my hobby painting miniatures, I've stuck to an old standard--painting my bases goblin green. Actually, the first thing I did was paint the surface of the base goblin green, and left the rim black (I was following advice given in the 3rd edition of the Warhammer Fantasy Battle rulebook, even though most of the models in the pictures had goblin green rims as well).
After a while I decided to up the complexity and I glued modelling grass onto the base surface--of course, it was a brilliant green, and so looked rather bright. (in the picture it has faded over the years):
I experimented briefly with modelling flock. The result came out ok, but I wasn't entirely satisfied with it.
I then tried gluing sand (or even gravel) to my bases and painting it. It took some practice but I got better at it. Here's one of my earlier attempts:
Eventually I settled in with that, gluing sand on the base and painting it entirely in goblin green, then drybrushing the base with Bilious Green (they don't make it anymore, the closest analogue is Scorpion Green) and then a lighter drybrush of Golden Yellow:
After a long time of that being my standard, I decided that my bases were too bland, so I decided to liven them up a little. Rather than pure grass, I would make it patchy grass, with the occasional rock and some static grass to give it some extra texture:
Nowadays the goblin green rims are starting to wear on me, so I've decided to liven things up a little. For a long time GW's minis have been sporting a neutral brown rim, and while at first I didn't like them, they're starting to grow on me. So I decided to do an experiment and see what colors would look good.Left to right the rims are: Calthan Brown, Graveyard Earth, Khemri Brown, and the original Goblin Green. Opinions? This next picture shows they'll actually look like on the gaming table: