Biggest wattage incandescant you can dig up should work. Supposedly they are all being phased out in favor of flourescents, which don't use as much energy per lumen, nor generate near as much heat. Sometimes that isn't such a good thing.
If you're out of incandescent light bulbs:
Depending on how many chicks and the brooder you're using, a heating pad (without an automatic shut-off feature) under approximately half of the brooder should help. The chicks can move to the other half if they get too hot, but it should provide enough heat (through, say, a rubbermaid/plastic storage container-type brooder) to hold you over until you can get another heat lamp. You might have to remove whatever substrate you're using (put down some paper towels), but a bunch of nasty paper towels is better than a box of dead chicks. Of course, you could always just crank up the heat in your house.
How old are the chicks? If they're even approaching fully-feathered, you've got a lot more leeway.