It depends on what do you use them for,because different softwares have different functions.Some are good at recording tutorials while others are in other fields.
1.Fraps--many people should have tried this one for game recording,you can try it too(not free,with with trial version)
2.Camtasia--a professional recorder that has lots of features to help recording(not free,with with trial version)
3.Camstudio--the only free one that i know,but i think it's not suitable for gaming recording since it's designed for tutorials recording.
4.Total Screen recorder--when recording something,it doesn't bring lags,but for games,not sure ,you may try. (not free,with with trial version)
5.hypercam-- quite good as well,for common recording.(not free,with with trial version)
6. FlashDemo screen recorder--Easy to use.(not free, with 15days free trial)
all the softwares,you can google and get them easily.
if you want to buy one,you can go to http://softseeking.com/prodail.aspx?proid=37
for spending less.