Since I felt it would be useful, I've compiled a list of sites to get brushes and fonts for all those sig-making quests.

First up, the Whole Damn Apple. They only have a few choices but they're very good quality. They're great for grunge.

http://damnapple.fredfarm.com

Next, an entire ring of sites for brushes. They have about 90 sites to search through. These are useful for any type of Photoshop.

http://www.ringsurf.com/netring?action=info&ring=psbrushes

Now, all the fonts you'll ever need in a nice tidy package.

http://www.1001freefonts.com
You'll also notice a pop-up for a large set of brushes for a small fee. You can download them if you don't feel like sorting through all the fonts on the above site.

Now, if you're one of the people who's taste can't be satisfied easily, you can always make your own brushes to fit your style. Simply browse the net to find a suitable picture you can see being used a brush. For this I recommend a large library of pictures found here:

http://creative.gettyimages.com/source/home/homeCreative.asp
Search "abstract" for some good grunge material.

Next, move it into Photoshop, right here you can adjust it any means necessary. Threshold is useful for making an interesting brush, to use Threshold go to Image-> Adjust-> Threshold. You can then change the Opacity of the Threshold if you'd like. Just go to Filter-> Fade Threshold.

Next, take the selection box and highlight the portion you feel you need. Next to the "Color/Swatches/Brushes" menu in the Brushes window, there should be a small black arrow. Click it and select "Define Brush". You should now have a new brush to use.