First came the picoPSU. Now there are bunch of similar PSUs - external power brick plus a small DC-DC board which goes inside the case. Perhaps it is time to have a sticky thread to keep track of them? (Even better would be a SPCR article.)
Here are some:
picoPSU: about 5 variants, 60-120W. The board is very small and attaches directly to the 20 pin ATX power plug.
M1-ATX and M2-ATX (3 models, 90-140W): intended for small PCs in cars. These are a moderate-sized circuit board.
PW series (4 models, 60-200W, moderate sized circuit board directly attached to 20 pin ATX plug.)
The manufacturer appears to be 'hifiatx', but I can't access their website because it demands a too-recent version of Flash. As a result, I'm unclear on what the non-brick part of this looks like.
PSB-1000. 150W? (No output specified, but they sell a 150W brick to go with it.) Smallish board with cable to 20 pin ATX connector, 4 pin extender (for 24pin motherboards) and hard-drives.