I am wanting to make a string of pearls to place coming out of a hat box cake. What is the best way to make these so they are uniform and perfectly round???

Use a mold.

Ok, if molds are not an option, what is the next best way?

Earlene has a how to on her website: http://www.earlenescakes.com/prlinstruct.htm
It gets them uniform, just takes a little time to get them round. But if it is at all possible, get some molds. Also I made my own pearl mold with plastique from makeyourownmolds.com. I think I bought a trial pack for less than the cost of one ready made mold and they work just as well. I did a graduated strand from a strand of wooden beads.

If you are doing them one by one I suggest that you use the back of a piping tip, roll your GP or fondant the same thicknes and use the tip as a cutter mold that way you have the same size ball everytime

Thank you. You all are very helpful.

Hammy I used the silicone plastique http://www.makeyourownmolds.com/silicone-plastique
At the time I bought it they had a smaller introductory offer for about $12.00. I just looked and they don't have that anymore. The smallest is 1 lb that would make a bunch of pearl molds. I just taped about a 6" section of the beads down on a plastic cutting matt, made a snake of the silicone and smooshed it down along the beads until it just about met on the bottom side and let it sit for about an hour. I had to do a little trim with the exacto knife to free some of the smaller beads. The mold is not at all pretty....kind of lumpy but it works just fine. I used it for the pearls on the platinum cake.

Thanks Dynee, I appreciate your help so much!
Hammy