What are the odds of flopping top pair? The odds of flopping a pair are about 1/3 I know, but that includes middle and bottom pair.

It seems very difficult to calculate, and I have no idea how.

I suppose that would depend what your hole cards are...the probability would change depending on what your highest card is

This would be a nice numbers analysis to prove out generally accpetable beliefs for starting hand requirements.

Seeing how the odds of hitting top pair go down with the declining value of your hole cards.

I'd be more concerned about the kicker the top pair comes with than the odds of it being flopped.
http://www.homepokergames.com/odds.php
in the Hand Matchups section places Top pair(bad kicker) vs Top pair (good Kicker) at 12.7% vs 87.3% underdog.

I'm not so sure this is even a calculable scenero without specific values known upfront. i.e if you had A-7o either could flop top pair but one would have a great kicker while the other has a lousy kicker. The odds of flopping either the A or the 7 could be calculated but how would you calculate 2 random unpaired pocket cards? Not sure it can be done.

Perhaps this is more useful - Here's the probability than your pair is going to be top pair when flopped:

K 84%
Q 70%
J 57%
T 45%
9 35%
8 26%
7 18%
6 12%
5 7%
4 3%
3 1%
2 0% (quads are the only way it's "top pair")