Mini-icons are essential when developing applications. Good icon sets should be visually nice but not too dominant, so they don’t steal the attention from the application. Good sets should be big enough to cover common application actions such as: add record, delete record, edit, save, Next, prev, mark as favorite, vote up, vote down, bullets, arrows…

When you need to quickly develop a prototype and get feedback, you probably don’t want to spend too much time looking for the perfect icon set. Save in advance the icon sets that you like, they will be very handy at time of need. Nice simple icons can make big difference in your prototype and add the wow factor. Later on you can decide to stick with them or have custom icons made by graphic designer for your application.

Many of the icon sets are free to use, check the exact license agreement in each site.

• Mini Pixel Icons
  Nice collection of 320 mini icons (14 x 14px)
  
• FamFamFam Silk icons
  Over 700 16-by-16 pixel icons
  
• PI Diagona Packc
  Another nice icon set
  
• Tango Icon Library
  Nice collection with several icon sizes
  
• Phoenity Aura
  Simple and sleek icons
  
• ASP.NET
  Free to use on ASP.NET web applications
  

And… if you need more fancy or unique icons check the following Icon Sites:

More icon resources:

• 20+ Free And Fresh Icon Sets
• Icons For Your Desktop and Icons For Your Web Designs
• 35 (Really) Incredible Free Icon Sets
• Free Developer Icon Sets
• 33+ Icon Resources For Commercial & Personal Use
• 101 Free Icon Sets that Kick Ass