You don't say what size you need. I used a 11.75"x6"x2" aluminium case from Maplin, it's perfect for a biscuit mobo, DC2DC power supply and a laptop harddrive. All you have to do is drill it for your air flow and connectors.
The link is (I have the PC25):
https://catalogue.maplin.co.uk/products/detailsframe.asp?SKU=1728&partcode=LF14Q:LH10L:LF1 0L:LF13P:XB71N:LF08J:LF16S:KR56L:XB69A:LF11M:KR55K :KR57M:LF12N:&cart=909133547&d=f&type=1& SecData=%5BeqSectiondata%5D&GroupData=METAL%20ENCL OSURES&SubGroup=GENERAL%20CASES
They also have larger cases to if this isn't big enough. Since they are aluminium, you can use it for heatsinking your PSU chips if you want (that's what I do).
-- <A HREF="http://www.nav.to/robwithey" TARGET=_blank>http://www.nav.to/robwithey