My (especially modding) interests go far, far far beyond cases. I only really have one case mod, but I'm putting everything into it. I figure, I only need one computer.
Anyway, among my dozens of other DIY interests, one has recently caught my eye: a low budget, creative, and actually fun one - Nerf guns.
You can modify they to shoot harder, faster and so on and so forth. Most guns can be bought for under $10, add spray paint and elbow grease and misc stuff and you have yourself a project. No custom cnc'ed grills and 1/8" plexiglass sheets or $1000 rigs with $2000 water cooling (though that's pretty sick, I don't want to spend that much money for some fun).
The part I liked is that, working around the shell, you can make it look like whatever you want. Add bondo and cardboard, and you're a plastic smith. A few guys have even gone the route of vacuforming (that is, using a vacuum to form softened plastic into virtually any shape). They even make their own darts.
These guys have "wars" or "nerf outs" where they play like paintball, just without the pain, the cost or the mess. It's like laser tag, just customizable, and the quality of your gear doesn't depend on how much money you dumped into it, but how much work and effort and skill was used.
So my first small projects turned out like this:
Nerf "Longshot" (front gun): Brown spray coat, weathered look in some spots, red and silver accents. I cut down the dead space, and around different parts as accents.
Nerf "Maverick": Russian Roulette (makes clip drop out and rotate freely) mod + took off black turret shell, added washer+nut to make up size difference. Makes a better seal.
"Big Blast" I added a couplered barrel (take it off, put a dart in, put barrel back on) and ammo holders. Holds 9 darts + 2 whistling missiles. Black sprayjob with brushed red accents (aka brushmarks are intentional).
This is just the beginning. Since it's not so cost intensive, I've taken on about 3 really big projects. Like I've mentioned elsewhere, soon I'll have a full sized workshop and more spare time. This summer is going to be awesome.