For awhile I collected (beer) bottle openers. That evolved from my hobby of home-brewing beer, which I haven't done much since my kids were born (almost 11 years ago now for the oldest!). It was cool to pick through thrift stores or flea markets looking for openers with interesting shapes or from obscure mfgs. Then, eBay came around and I saw I could find a gazillion of them, just pay the money. That took the fun out of it.

I also have a nice collection of late 19th/early 20th century handbooks on technical writing and basic rhetorics. That has to do with my day job.

Neal