There's loads of things, to be honest I never really feel down, I'm always quite positive and look on the bright side of things, life's too short to be miserable.
A lot of mine are food and drink related though.
Trying a new beer and it being amazing, I try to have a different beer every time I have a drink (providing I'm in a decent ale pub), you're bound to get some that aren't brilliant and some that are average but when you get a really great one it's fantastic.
Cooking for other people and seeing them really enjoy it. I also like it when you "convert" someone, my wife hated fish when we met (as she'd never had it fresh or well cooked), she now enjoys fish and part of that is from trying dishes I'd made. I love it when I serve up a fish dish and she loves it.
When you order a dish in a restaurant and it comes out and the presentation is great and you just smile to yourself.
Popping candy!
Hearing a new song for the first time and absolutely loving it on first listen.
Going to a gig and just being totally into it, just standing there and being totally into the music.
When you have a busy calendar on your phone and you look at it and realise you've tonnes to look forward to.
When my son does something new or interesting.