You can get an SFX(many times mis-labeled as mATX) power supplies upto 450 watts(I have seen higher, but do not trust the makers.).
Silverstone has a 450 watt 80+ bronze non modular and for a bit more an 80+ gold modular.
Bronze
http://www.silverstonetek.com/product.php?pid=253&area=
Gold
http://www.silverstonetek.com/product.php?pid=342
My only word of caution on the Gold model is the space the modular plugs take. As long as that is not an issue, the lower heat output of the gold model can reduce the noise in the system as well as the power it takes to run.
Many users seem to like the SG05 from silverstone for a small system, you can get bigger and smaller from silverstone/coolermaster/Antec/Fractal/ect.
You have LOTS of case options.
Careful part selection is critical in small cases as well. Notebook drives and SSD's save space/heat and power.
If you want to use a normal power supply, do not mind the lack of a optical drive or longer video cards, you can even get this little guy
Elite 110 by CoolerMaster