No, don't get him an iPad, just the cute "who ate my apple" decals for the back. There are also versions for the other Mac computers. $9. (Apparently my own father, who can't even figure out the contact list on a cell phone, is getting an iPad for his birthday at the end of the month. I'll let you know how THAT goes...)
How about a lovely black and white baseball photo? An 8x10 is $20, unframed.
My parents have given me cards with money inside over the years, and I've always thought it would be hilarious to do it back. Hand-stitched card (without the money), $6.
What are you getting your dad? I'm getting mine a case for the forthcoming iPad. Sigh...