Generally i would go the all natural route of a fishless cycle with maybe a few plants, or small feeder guppies... However if your in an absolute rush to get it going, there are several products out there that claim to do an "Instant Cycle" and ive tried many in my marine studies classes, only to find select few that sort of work, and one that actually has worked for me on several occasions by the name of FRITZ-Zyme Turbo Start 700.... If a petshop has it, it is going to be in a fridge, since it must be refrigerated to keep the bacteria dormant... ive tried it on a few test tanks, all fishless and all started at the same time, with the same media, same filter, same water treatments etc. 4 tanks, we of course had our control and our variables, 9 times out of 10 with the other "Instant Cycle" products, they are more of a snake oil per-se but this stuff actually seemed to work, building a nice bacteria colony rather quickly, granted the little 1 fluid ounce bottle is meant for a 40 gallon tank, you can safely use up to 5 times the recommended amount supposedly and be fine, though ive never tested this, ive used the whole bottle on several 20-40 gallon tanks after several of our tanks became "Un-Cycled" in our marine lab, and 2 or more bottles for larger tanks depending on the size of the tank... The stuff can be a bit pricey for its volume, usually in the 10-12$ range... I would still recommend waiting atleast a week or so after adding this product before adding any animals you WANT to be in the tank, aside from cycling aids that you may wish to use, and do daily - bi-daily water checks to insure its working... The product has a 3 month shelf life (being in the fridge that is) it also works for controlling an ammonia spikes or nitrite spikes
Hope this helps and good luck with your new tank