what type of resistor is required for LED indicators?

[aussiemonster]

Bought some LED indicators off Ebay and a set of resistors to make them flash the right speed. Indicators work, resistors didn't.

I'm guessing the resistor was too strong as when I added it the indicator didn't flash at all, removed it flashed too quickly (as expected).

So...

Anyone know what size resistor is required to make LED indicators flash at something close to the right speed?

Cheers

Dale