I collect vintage firefighter items. Both of my grandfathers and my father were firefighters. Right now I am sticking to badges and other smaller items until we move and then I will expand once my man-cave is up and going.
My other main collection is books. I collect first editions from authors like Dean Koontz and a few others. I like to find the rare items, like first editions published under pen names and early books before the authors were big names. My wife found me an early Koontz edition that was listed incorrectly on eBay. She picked it up for $5.00 and it is currently worth in the area of $500.00. That was a good birthday.
Years ago I was an avid collector of vintage Star Wars items but I eventually sold off my entire collection. It was getting harder to find with eBay up and running.