For sponging on the gradient you can buy a nail art sponge kit but I find that those foam makeup wedges work great for me. Doing this can be messy so be sure that you have lots of qtips and acetone! Also, after it was all said and done, I decided to add irredescent glitter from Sally girl to each nail. The 2nd pic does not do these nails justice. They looked 10x better in person. My camera is a cheap Kodak Easyshare so the bright colors do not shine through! I still loved them and rocked them for Thanksgiving day.
One other tip with gradient is to put the top color and bottom colors on first and then blend them with the middle color, especially if the middle color is darker than the other two colors. You also want to be sure you use a thin line of sponge with the middle color or it can take over the whole nail like it does with mine. Happy gradients, people!