This might sound a daft call, but I've got into restoring old school bmx bikes.
Theres parts aplenty, but sometimes hunting down the "right part" is a bit of a challenge, and many require restoring. But finding a frame and forks, doing the acid path, possibly sending for rechroming or powder coating, and refurishing a nice bike is satisfying, and requiring slightly different(but simpler) skills to usual bike maintanace.
I've got 4 on the go at the moment, and the fun of making a new set of bike contacts, swapping parts, making newcontacts and being able at some time to actually ride the fruit of your labours is great!
Race you on my Harry Learyalike Diamond Back Senior Pro with Leary Pro bars and a DB Formula1 crank.