If you are looking to get some interesting, fairly unique bases for your army and want a consistent theme but dont want to spend hours making bases, then resin bases are an excellent choice. Resin bases are simply casts of terrain and textures on standard sized bases made in resin (what a shock!)
Working with Resin Bases
Resin often needs cleaning and trimming but is usually easy to work with and has a similar feel to working with plastic. When gluing, do not use plastic glue (polystyrene cement), instead stick with superglue or something stronger. Some companies use a heavier type of resin which is very hard to drill for pinning, so be careful and stick with glue where possible. When filing resin be sure to do it in a ventilated area as many types of resin are very bad for you if you breath them in and it is very easy to do so when filing at speed.
For more information on working with resin bases, check out the article on Using Resin Bases.
Resin Base Stores
Here are some of the options for resin bases that are available online.
A more complete list including updates on new releases by them can be found in this thread:
Back 2 Base-ix
epicast also available at:
Evil Mushroom Games
Micro Art Studio Bases
Wargames Workshop Bases
also carry micro art studio bases
Kerr and King Bases
Kerr and King (a UK based resin basing company) make bases suitable for Warhammer 40k, Fantasy, Warmachine (including wreck markers), and Flames of War.
Iron Halo Bases
Iron Halo puts out a series of Fantasy, Warhammer 40k bases as well as inserts for Warmachine / Hordes bases.
Dark Art Miniatures
Dark Art Miniatures bases are 100% resin cast with no fillers. More bases and terrain pieces available at the Dark Art Miniatures webstore. Painting guides and other information can be found on our website.
Model Display Products
More bases and terrain pieces available at the following http://www.modeldisplayproducts.co.uk/
Making Your Own
One other option for resin bases is to simply make your own. Resin casting kits can be found in many art stores and allow you to make silicon molds from your own home-made bases. You can then cast as many bases as you want from those molds allowing large numbers of similar bases to be created for your armies!
More Resin Base Companies
A comprehensive list of resin base companies can be found in this thread in the dakka forums.