I’m generally a happy guy, but for pick-me-uppers the Meat Puppets are at the top of my list. The deep/strange/etc lyrics and twanginess of the music just makes it hard to be depressed.
As for Dinosaur Jr, I’m not sure if it’s ever really cheered me up, but it’s helped get me through some tough times. Keep in mind that I haven’t been into them for all that long, and that I generally don’t turn to music as a primary means to pick me up. Not to say it doesn’t help, though.
EDIT: Now that I think more about it, Green Mind does cheer me up a bit from time to time primarily due to the overall feel of the album as well as some personal memories that I associate with the album.