This is a list of a good brushes to help you create your signatures. If you have one that you think is worth posting, please PM me and I will add it to the list!

Jashins Brushes Set 14
Caffine
Blind's Grunge Set 1
Destiny952 Set 60 Old School
Destiny Abstract Chaos Set 2

HOW TO INSTALL DOWNLOADED BRUSHES

After you have downloaded the file, unzip it to the following directory:
Program Files --> Adobe --> Photoshop --> Presets --> Brushes
Open Photoshop and from your brush menu choose 'Load Brushes' and from the list which will open, choose the brush you would like to load.

Alternatively, go to the brush menu, select replace brushes, and browse to the directory that you downloaded to and open.