Deli shrimp is coctail shrimp just like you eat at parties. It adds an ammonia source that jump starts your cycle.
The better your water, the more LR and LS you have, the shorter the cycle IMHO.
I agree with BigAl that you should test your water daily (preferably at the same time of day) and keep a written log of your results. You can even start a tank chronicle on RS to store you tests.
I suggest not using live fish for the cycle. It's unneccarily cruel and no better than using a deli shrimp.
I'm guessing you are asking because you are in a cycle right now waiting for your tank to finish. You could use this time to thoroughly research your stocking list, save money for future equipment, get in the habit of testing your water (and perfecting your technique,) and practice that wonderful trait that all reefers need....patience.
It's not uncommon for a tank to take up to two months to cycle. I've read, and agree, that you should not do water changes or run a UV filter during the cycle. These normally beneficial things can actually slow down the initial cycle.