I don't want to hijack the thread since my official sketch cards aren't sports-related, you can see all of my work at the link in my signature.
The only "official" sports artwork I've done is paint a Phanatic statue for the Phillies that raised over $14,000 for their charities. :)
Here are some pieces I've done that I've gotten signed in-person.
Penn & Teller
(Penn signed it on the bottom left, hard to make out)
That 1 Guy
Jack Nicklaus (I don't own this, someone I drew it for got it signed)
Here's a rundown of the program:
And here's the dedicated site to it:
If you go there and click on the About the Artists button, make sure you check me out on the list -...