These are some of the most popular websites for downloading presets. The presets listed here are a mix of PV2012 (Lr4/5) and earlier (PV2010/2003), and I’ve split them into Free vs. Paid to help your search. If you know of any more that you think should be included, please let me know. Enjoy!
Lightroom Killer Tips (Matt Kloskowski)
Free Lightroom Presets (free sign up required)
Free & Paid Presets
The Preset Factory – 25% off with LRQUEEN25
Only Paid Presets
Really Nice Images (film emulation… very good!)