thought i should add, for parties and such, you can just use a flash. a good bounce/swivel head starts around $200 (original 430ex, Sigma 500 Super). a simple bounce head is a little cheaper - $150 for the 270ex, which i think is the most expensive.
for reference, the 35mm f/2 is the cheapest of the fast, wide-angle primes, and it costs $250 new. also, you lose flexibility over working distance, depth of field, amount of light, and quality of light.
Some places dont allow for flash inside, but i havent ever really shot high school (or whatnot) sports.
And i wish there was a lens for ever occasion.... a 10-800mm f/1.8 IS , hell lets make it f/1.0..i mean it will already weigh like 80 LBS as the Canon 1200mm weighs in at 50+ lbs, but there are only 7 in existance i believe, and SI has 2 of them.....