First ever tab! Not actually mine, I got it from heartwoodguitar.com. This song is GENIUS 
http://www.youtube.com/watch?v=cIy-_1KkDrM
Intro:  / G - - - / - - - - /
 
G (2)
Once a year we celebrate
          C                     G
With stupid hats and plastic plates
         G (2)
The fact that you were able to make
              C        G (hold)
Another trip around the sun
G (2)
And the whole clan gathers round
        C                       G
And gifts and laughter do abound
       G (2)
And we let out a joyful sound
       C                      G (hold)
And sing that stupid song
    G            C             G (2)
Happy birthday!  Now you're one year older!
    G            C             G (2)
Happy birthday!  Your life still isn't over!
    G           C              G
Happy birthday!  You did not accomplish much
 G (2)
But you didn't die this year
    C               G
I guess that's good enough
 
/ G - - - / - - - - / C - - - / G (hold) /
    G (2)
So let's drink to your fading health
    C              G
And hope you don't remind yourself
     G (2)
The chance of finding fame and wealth
     C              G (hold)
Decrease with every year
    G (2)
Does it feel like you're doing laps
        C           G
And eating food and taking naps
    G (2)
And hoping that someday perhaps
     C                   G (hold)
Your life will hold some cheer
     G           C                      G (2)
Happy birthday!  What have you done that matters?
     G           C                      G (2)
Happy birthday!  You're starting to get fatter
     G                 C            G
Happy birthday!  It's downhill from now on
   G (2)
Try not to remind yourself
    C               G
Your best years are all gone
/ G - - - / - - - - / C - - - / G (hold) /
 
  G (2)
If cryogenics were all free
     C                   G
Then you could live like Walt Disney
    G (2)
And live for all eternity
 C                G (hold)
Inside a block of ice
 G (2)
But instead your time is set
     C           G
This is the only life you get
    G (2)
And though it hasn't ended yet
    
     C                 G (hold)
Sometimes you wish it might
      G              C                 G (2)
Happy birthday!  You wish you had more money
      G              C                    G (2)
Happy birthday!  Your life's so sad it's funny
      G              C                 G
Happy birthday!  How much more can you take?
  G (2)
But your friends are hungry
        C              G
So just cut the stupid cake
           G (2)                      A7 (2)
Happy birthday!  Happy birthday!
           C (2)         D7 (2)
Happy birthday, dear...