I really like  story so far's pop punk band from California 
Oh yeah! How long have they been around?
They formed in 2007, I listened to them cause they sounded like Blink-182
I haven't ever heard of them before, but admittedly it's not a genre I listen to much. Have they sold a lot of records?
Yeah they are pretty regional, they have released 3 records so far, but not a multi platinum artist.
What is a good song of theirs that I should listen to in order to get familiar with them?
In march of 2013 they released their second album "What you don't see". That was number 46 on the Billboard 200 you should start there.
Sounds good! Do they ever collaborate with any other artists, or do they just do their own thing?
Sometimes they do cover songs like Pinkback's song "Loro". But other than that no collaborations.
I do enjoy me a good cover. It's nice when a band from one genre covers a song from a completely different genre, and you get to enjoy a new take on the same old song.