If you've upgraded to Snow Leopard then one thing you'll notice that hasn't changed in the new OS is the style of icons.
However, you can change this yourself courtesy of icon collections such as nuoveXT 2 which is actually a cross-platform icon development project. These sets of icons have been designed specifically for Mac OS X using a design app called Inkscape. This pack is known as IContainer and for ease of use, it's probably best to use an application like CandyBar. The reason for this is that there are 59 icons to choose from ranging from art and photo related folder icons to those with a Web and video theme.
nuoveXT 2 for Mac OS X is a useful collection of 59 icons although there's nothing outstanding or particularly imaginative in here.