I suspect every mom has done this at least once: you get the presents out of wherever you have stashed them, and make a pile for each kid so you can wrap them...and then realize oops, one kid has a lot more than the others.
I think this especially becomes a problem when your kids' interests start to diverge, with one leaning more toward "big-kid" wants and the other still into toys. For example, my daughter wants an iPod or Nintendo DS this year, while my son wants a remote control monster truck, some Legos, a toy garbage truck (I don't even know where to begin, there) and some race cars. His pile would be a lot bigger than hers unless I totally blow my budget to even up the present count.She's kind of at the tail end of the Santa years, too, so I can't explain it from a budgetary standpoint.
I'm getting around this by giving her my old iPod Touch and buying her fancy earphones and a gift card for apps, thus making the unwrapping equal and my budget unblown. But this might be the last year I can get away with that. I know some families do the "Victorian four": something you want, something you need, something to wear and something to read, while others do three gifts, for the Three Kings, which are good ideas too.
How do you keep the present distribution fair?