How many teeth are on your rear sprocket?
Let's put it simply: When you pedal once you spin the rear wheel a certain number of times.
STANDARD: 1 pedal spins the back wheel 2.75 times.
If you have a rear sprocket that is 16 teeth, then you would have a 44 tooth sprocket up front. (16 x 2.75 = 44) For years and years and years that was all that you could get on bikes.
Now though people run smaller sprockets in the back than 16 teeth so they can use smaller sprockets up front. For example, I run 30/12 which is a little easier to pedal than 44/16. If I wanted it to be the same I would run a 33 tooth sprocket up front which is 12 x 2.75. 30/12 is still pretty good for getting around town though.
The smaller your sprocket is, the easier it will be to pedal. You don't want to go under 2.5 times your rear sprocket size if you still are going to be travelling around town, and you really don't want to go above 2.75 times your rear sprocket size if you aren't racing or full of the crazy musclely legs.
Also, if you need larger sprockets, www.danscomp.com
has a long list of larger sizes, but none of the really small ones like flatlandfuel has.