Groundwork
I've not attempted too many bases for my finished models and the ones I have had made have been minimal affairs utilising items I've found about the house. Old wooden name plates and even an Ikea shelf! Not the best looking or ideal material but they have been a test bed.
I have slowly been acquiring various groundwork products such as cheap picture frames, clays and sculpting materials, vegetation, ground mats and the like. To date I have only used a few of these materials on the bases I mentioned above, and these have been very small affairs showing road/track sections for wheeled vehicles. As for buildings I have messed around with a selection of Miniart's vacuum products but didn't get on with them too well!
I now need to learn the basics and find out which adhesives bond with which materials best and how to construct a base from scratch. I have plenty of vignette/diorama ideas of which many are sketched so putting them into practice is the next step.