Ive tried a handful of dice apps, and this is by far the best. Youre able to roll a good number of dice, add a modifier and go to town.
It can do nonstandard die types (d5, for example) and so works as a random number generator as well. Fantastic UI, with a really clever faux-3d look.
The developer has also said that the ability to lock dice is coming in the next release. Pretty great. Worth a dollar, easy.
Skinnyghost about Mach Dice