Man, that's a wild looking case! Yeah, tough to find mATX cases at all, let alone having a decent selection. There's a benefit to larger mATX cases - many take standard ATX power supplies. Basically they're just a couple inches shorter and less deep than regular towers. There are smaller cases but those have drawbacks such as proprietary power supplies, plus some of the cases don't take normal height expansion cards.
Aopen DeskTop mATX Case Model H340D Black
This $37 case/power supply is also available in beige. I actually have one of these cases (but have yet to use it). It looks nice and is a really small desktop size. The power supply is proprietary and puts out 200W, is very quiet and seems reasonable quality (heavy).
PRO: small, attractive, inexpensive, USB 2.0 ports in front
CON: proprietary power supply, non-standard expansion card height, floppy drive faceplate (IMO)
AOPEN Model# H450 w/250W POWER SUPPLY
Another AOpen case available in black or beige. I've never seen this case in person, but it looks decent and uses a standard power supply. Not a bad deal at $45, but is also not too small in size. However, it is a true mATX case, and thus still a bit smaller than any ATX case.
InWin Model IW-V523
There are a few versions of this chassis available, for around $40 each. There are the black ones and the beige/grey ones. Different plastic front for the two color schemes but the internal chassis seems the same nice heavy-guage metal. The newest black one is toolless and looks to have a side vent over the CPU (to get Intel 3.06GHz certification perhaps???). The power supply is a "shorty" ATX model rated at 180W, but a normal ATX power supply can be shoehorned into the case if your CDROM drives aren't too deep. I've built one of these (highly modified) for a friend and used a second one for my GF. This case also has some of the best ventilation in any case I've personally worked on (before modification). I like this case.
PRO: heavy duty thick metal, standard ATX power supply "can" be used, really REALLY good ventilation, smallest of the "standard sized" mATX towers (using all standard sized parts)
CON: seems perpetually out of stock, floppy drive faceplate (IMO)
INWIN MICRO ATX MINI TOWER CASE (Blue), MODEL# IW-L545P
This case is available in a few different colors. It is the narrowest case possible to still fit standard height expansion cards. Couple of things I don't like about it is proprietary power supply, CDROM sideways mounting, floppy drive faceplate. Still, not bad for $38.
Lite-On Model# BK 202 (Black)Micro ATX Case w/ 200W P4 Ready Power Supply and Front USB Ports
This case reminds me of the desktop AOpen case, with similar design. $36.
FOXCONN Model# TM-163 (BLACK)
This nice looking $38 case claims "INTEL Approved Chassis 3Ghz+." I believe it does so by a side panel duct to allow cool air to be sucked directly onto the HSF. Makes me think of old overclocking tricks with ducting and such. There is a beige version of this same case that is a better deal at $39.99 at Newegg.com with FREE SHIPPING. Most cases will run $10-15 shipping. This case comes with a 250W normal size ATX power supply. It has a nice clean look, not too wild and not too conservative. With the side duct the CPU temperature should be nice and low (as long as nothing blocks the duct). I've never used this case but look forward to trying it out soon.