Music is best when it comes from somewhere that inspires passion. I find music inspired by happiness tends to be... well, hokey. That said, I spent one summer listening almost exclusively to: Nada Surf's The Weight Is A Gift, Maritime's We The Vehicles, and Harvey Danger's Where Have All The Merrymakers Gone, which aren't necessarily happy records as much as they are fun, poppy, and not miserable. Definitely recommended on all three.
Also, music that makes me happy isn't always music that IS happy. Listening to McLusky Do Dallas, or Death Grips' Exmilitary, or Trap Them's Darker Handcraft all make me feel like jumping and punching myself in the face, but, in a great way.