Ok, I'll try to define what I call High Fantasy (or at least what I would, if I used that term often)...
First, you have to have epic plots. And by epic, I mean world-changing, spanning over whole continents, and so on, rather than 'above level 20'. Ususally, good epic plots are given extra drama with challenges of the mundane sort as well, like having to find somewhere to camp for the night on the way to find the "evil widget of doom".
Second, you need the element of good vs. evil; that's the main thing that makes it 'high' fantasy instead of 'regular' or 'low'.
Third, you need the classic elements that Felix mentioned.
Fourth, you need 'fantastic creatures,' like dragons, trolls, and other more original creatures.
Last, you need verisimilitude. Everything has to fit with everything else. You can't explain away impossible climates with 'magic' or 'the gods' in high fantasy if everything else has a scientific basis. You can't have magic shops and witch-burnings in the same town (except in strange circumstances, of course). You have to have things fit together in high fantasy.