I used to collect coins, my dad got me into it, but I haven't added anything to my collection for several years now. I have almost complete sets of Mercury dimes, standing liberties, Jefferson nickels, Kennedy halves, Morgan dollars, Lincoln pennies, and several other US coins.
My favorite coin is a 1909 S-VDB penny. It's by far the most valuable Lincoln penny, worth around 500 bucks I think. My dad told me about it and how rare it was a long time ago and as a kid, obviously that one rarest coin became my focus. Every coin show he'd take me to, I'd scour the place and I eventually found one that had been mistakenly put in a bargain box, which is pretty unbelievable. I ended up telling the guy and offering him a hundred bucks for it, which he agreed to (possibly 'cause I was like 12 years old), and was still a steal for me.
-J