Back in the day (circa '97) the fantabulous Dell Dimension cases were sourced from Palo Alto Systems. PAS cases are hard to find in the retail channel, but they're out there. They're really nice cases and I believe Dell still sources most of their cases from them.
Of course, you can always get a phatty aluminum case and make Dell owners fume with case envy.
Tyan Tiger MP | 2 x Athlon 1.2 Ghz
512 MB Crucial Reg ECC DDR | Intel Pro 100
80 GB Seagate Baracuda ATA IV | GF4 Ti 4200
Hercules Muse XL | Hauppauge WinTV
Antec 400 watt PS
all in a Coolermaster ATC 200 running Gentoo