Photoshop brushes are AWESOME!!! I just discovered them and have been playing with them for two days straight.

They're like rubber stamps on steroids. You can control the brush dynamics - the separation of each individual "stamp", the color and brightness "jitter", randomness, edges, etc.

I've found many sites that offer free brush sets, but

Truly-Sarah.com

and

AnnikaVonHoldt.com

are my current favorites. AnnikaVonHoldt's brushes are like instant creativity! You will be creating beautiful and mysterious fantasy images almost automatically.

Update: the Truly-sarah.com site is no longer online, but some of her brushes can be found at trulysarah.deviantart.com

My first attempt using brushes from these sites: