He broke into Penny's apartment just to clean her room!!!!!! He has soo got OCD!

Hhehehehe. I just watched that! Lolz Hillarious!

Everytime he knocks on Penny's door it has to be the same pattern of knocks and "Penny"'s!

Knok Knok Knok PENNY!!!
Knok Knok Knok PENNY!!!
Knok Knok Knok PENNY!!!
I also do things in three's due to OCD!!!
OCD is Not Funny!!! 8(
But Sheldon is Awesome!!! 8)

He also does the samethings over and over again

Well, lets see. He organizes his cereal by fiber content, feels the need to clean Penny's apartment even though its not his, has a particular knock pattern, does the same things every night...
Nawwwww... ;)

I think he has OCPD.

If Sheldon had OCD, he would go to the bathroom at specific times.
If Sheldon had OCPD, he would make Leonard also go to the bathroom at specific times.

So, yeah, it's SO OCPD.

I liked that they finally made an episode where he was confronted about his need to finish things. I'm not sure if it's ever been confirmed exactly which disorders he has, but in addition to OCD it's also suggested that he is autistic due to his difficulty with recognising sarcasm.