The Cubs have Go Cubs Go.
Is this common? Do other MLB teams have (official or otherwise) team songs?
Was the Beatles’ “I’m a Loser” already taken? 
Tessie is as official as a Red Sox xong gets, even though they play the Standells’ “Dirty Water” after a win. The original version, from the 1903 World Series, is pretty cute, but the Dropkick Murphy’s version
The Indians have Tribe Time Now, which I don’t particularly like. The extended version that gets played when there’s a rain delay and the announcers aren’t punctual is particularly tedious.
We also have Indian Fever, which is older and completely lame…but I have a soft spot for it.
Go Go You Pilots is so damn catchy it makes me want me to go see a Seattle Pilots game. Too bad the team moved to Milwaukee in 1970.
The St. Louis Cardinals actually did come up with an official song about 40 years ago, but it never caught on. The unofficial song, of course, is “Here Comes the King” otherwise known as the Budweiser jingle.
The Blue Jays have had an official team song, “OK Blue Jays,” since 1983.
The Angels had a team song, “California Angels A-OK!,” which later became “Anaheim Angels A-OK!” when the team name changed. (“Anaheim” was stretched out into four syllables to fit the tune.) I don’t know if they still use it- “Los Angeles Angels of Anaheim, A-OK!” would be pretty rough to fit into the song.
There are also songs composed by Terry Cashman of “Talkin’ Baseball: Mickey and the Duke” fame.
He wrote and sang “Talkin’ Baseball: Forever Dodger Blue” and did songs for other teams too.
It’s not lame! It takes me back to the '70s and '80s! Kuiper, Blyleven, Charboneau, Buddy Bell . . . Indian Fever, Be a Believer in the Cleveland In-di-ans!
I’m pretty sure no one else in the league plays “Deep in the Heart of Texas” in the seventh inning stretch… 
(Houston Astros)
The Cubs also have “Hey Hey Holy Mackerel,” written in 1969.
“Hey, hey, holy mackerel,
No doubt about it,
The Cubs are on their way (hey, hey)
The Cubs are going to hit today,
They’re gonna pitch today,
They’re gonna field today,
Come what may the Cubs are gonna win today!”
We wrote a parody version in 8th grade entitled, “Indian Seizure”.
You will recall the song started
“Indian Fever! It starts in the very first inning…”
We which changed to
“Indian Seizure! We sure wish we were winning…”
It went on from there. Good times. 
I don’t think the Braves have a song, but they are AFAIK the only (real) team to be mentioned in an episode of Star Trek.
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I am as diehard a Cubs fan as one can get, and I hate that song with the bright candlepower of a billion searchlights. I think the reason we lost for so long is so that nobody would have to hear that retchingly awful tune.