http://www.introversion.co.uk. I played Defcon and Uplink and both are absolutely excellent games. Darwinia was a tad abstract for me but the other two are awesome.
Also try www.matrixgames.com for their stuff which is often made by a couple of guys in their bedrooms.
One of my favourite games ever is also manufactured by a small concern. A superb wargame on the 2nd Battle of Manassas. www.madminutegames.com
There are a few kicking around although they tend to be in the "grog" wargaming community. Which suits me fine!