Talysman over at The Nine and Thirty Kingdoms has a nice little series of blog posts on traps.
If you ever wondered what a pressure plate could look like, mechanically, or how a tripwire might work, this is a good place to look. The posts have gaming-oriented discussion, ideas about construction, and nice pictures if (like I am) you're more visual than text-oriented when it comes to visualizing.
The posts are aimed at AD&D/OSR style gaming, where pretty much nobody has skills and many referees seem to follow the "describe how your searching and I'll tell you what you see" approach. I use a skill-based system, so I don't need quite so much information about how to detect and disarm the traps. I get to just have people roll. But it's entertaining and useful information nonetheless, because:
a) I do hand out bonuses for describing what you're doing. Disarming a -0 trap takes a flat skill roll. Disarming it after you carefully describe how you're doing it nets you at least a +1, usually higher, because describing how you do things makes the game more awesome.*
b) I have to describe how the damn thing worked when you disarm it, or cast a spell to let you see through the walls and spot the mechanism, and other such fun.
I once got a whole book on outdoor survival just for its nice section on trapping animals, and used those descriptions of deadfalls, trip lines, and foot snares to describe my horde pygmy traps in my previous long-running GURPS game. I'm a big fan of traps, and how they work - the more description I have for them, the better, because my players are pretty meticulous about avoiding them (and so very few have any Traps skill, so they really tend to work hard to get those bonuses).
Speaking of traps resources, I own both Grimtooth's Traps books, too (and FWIW, the first GT book is back in "print" now). But I don't have much beyond that. If anyone has recommendations . . . put them in the comments please!
* See "the rule of awesome" for why that's important. Having good stuff happen in return for doing cool stuff and for getting your head into the scene is also awesome, IMO.