It can be both easy or very stressful finding plugings for photoshop. For the hard ones, here’s a list to help you:

• virtualPhotographer
  Plugin that allows you to cut our pictures with various effects with just a few clicks.
• Richard Drosenman
  This site offers a wide range of plugins, some functions are already included in photoshop by default but there plugins are easier to configure.
• Filter Forge
  Allows you to create your own filters, it’s a trial program that will only last 30 days, but your filters will be forever.
• Harry’s Filters
  It brings along 69 different effects for your images. They will let you select the type without so many menus nor options, they’re all separated by categories.
• AutoFX Mosaic
  Another “reloaded effect” for photoshop, the Mosaic filter allows you to generate Mosaic images.
• Auto FX Dreamy Photo
  Give your pictures a “romantic touch” with this plugin, actually this plugin gives an unfocused look to certain areas with dim light.
• Telegraphics
  A great site with tons of plugins, also for illustrator and many more things.
• Xero Graphics
  4 sets with 9 plugins each
• Free Photoshop
  High quality plugins available for downloading.
• HDR Soft
  This is a great plugin that will let your pictures have more vivacity and brightness.
• Luce
  Add advanced shadowing effects to your texts and images.
• FlamingPear
  Great trials for downloading.
• Mehdi Plugins
  More plugins!!!!!! El ZoomEngine seems interesting, a great tool to avoid the blurring that happens when you try to zoom an image.
• Little Ink Pot
  Various plugins
• Mura’s Filters
  Filters for clouds, perspectives and more.
• Plugins World
  A plugins search engine for both free and paid ones.
• Vanderlee
  More options for plugins, like halftone, to make images look like an old movie or night vision or like camouflage.
• Pog’s Notes
  Free plugin collection.
• Photo Plugins
  Plugins orientated to image quality editing.

Source: InfectedFX