I have two machines...
The first I purchased was a Williams "Black Knight" Limited Edition. I bought it because I pushed many quarters into it, after having spent many a long night of studying in the student union. It brings back memories!
My second is another Williams pinball, "The Getaway: High Speed II" (Second Revision, which has the Diamond Plate playfield.)
I'm a Electrical Engineer, so they appeal to me, as they are electronics that I can actually work on and fix, without needing a stereo microscope, and tweezers to handle the components. I enjoy playing them, fixing them up, and the occasional bit of modification to fix issues with their designs.
The Texas Pinball Festival here in Dallas is always a lot of fun. A chance to play lots of pinball machines. Last time I saw a Williams Joust Pinball machine (not the arcade game, the pinball machine, production run of only 402), which is incredibly unique, in that you can play head to head against another player. The festival always has lots of machines up for sale as well, and lots of vendors selling parts. I notice they don't have much info up yet on their website, but here's the link: http://www.texaspinball.com/
If you should decide to come for the pinball festival, give me a heads up. With all the enjoyment and info I've gained from your site, seems like I owe you a nice steak, beer, and to play some pinball.