Presets are an important aspect of photography post production. Presets can massively speed up the process of getting your photos ready for the public eye and are also a great source of learning. When I started with Lightroom 2 I worked with many of the free Lightroom presets that were available before moving to creating my own custom processes.
If you are new to lightroom 2 or 3 then check out this post on how to install processing presets. Here is a list of some of the sites I have used to gather up some custom (and free) lightroom presets.
Flickr : 180+ Free Presets for Lightroom
Presets by Katherine
I brake for Bokeh and Presets
Skyes the Limit
The 300 Preset
A Girl in Love with Photography
Dror Eyal Photography
28 Free Presets from Chris
27 Free Lightroom Presets
35 Free Presets from Speckyboy
Cameradojo (Lightroom 2 but they work in 3).
Vivian Chung Presets
Help with Presets
I would recommend you regularly carry out some preset house keeping. It is amazing the number of unused presets that end up cluttering your interface. If you haven’t used it up to now, chances are you never will.
If you want to know how to create your own presets you can follow this tutorial on how to create a lightroom preset. If you are an advanced user and are into camera emulation then check out how to go about creating some emulations lightroom presets.