Here is a list of links where you can get icons which are of Web 2.0 standard and which are royalty free for personal and non-commercial use. Each of these icon providers develops icons for different purposes and with different themes. There are icons for OS, Vista, Desktop, Browsers, Docks, Toolbars, Blogs, Web and for everything.
Free Web Icons
Free Web Icons is one of among the places where you can get high quality icons with web 2.0 look for free. They have over 15000 icons to play with.
Web Site Icons
Web Site Icons is another site which has a huge repository of icons with varied themes. They have around 110 sets of icons. So you name it and they have it!
Vista Icons
Vista Icons have a collection of icons which are distinct from others but which has a similarity with Vista look. Their collection of 8 different themes are a must try.
Iconoholic
Iconoholic provides icons which are themed like U Torrent, Bit Torrent, GTalk or Gmail and all that accounts to 22 different sets. They also provide themes for windows as well as Wallpapers.
Dock Icons
These are the list of icons which are exclusively used with dock programs from devianart.
Tool Bar Icons by Matt Ball
These royalty free toolbar icons can be used in your browsers and wherever there is a toolbar.
Free Aqua Glass Icons
Dezinerfolio has a set of 32 icons with aqua glass look and they look really amazing. These can be used in blogs and he also has a huge list of buttons for blogs.
Crystal Clear Icons
These icons are listed in Wikimedia and they have a huge number of icons listed and designed to symbolize different purpose like Actions, Applications, Devices, File System, KDE and MIME Types.
Tango Icon Gallery
Last but not the least, this is truly the place where you can get icons of all shapes and sizes for all seasons and reasons. I started to count the number of icons they have but I gave up as I couldn’t finish it up!
This post is written in participation of the Blog Project: Three from Daily Blog Tips. I couldn’t fit this topic withing three, so I made it three times three 
This is a great compilation buddy! I’m going to have fun looking at all of these
huge collection ! Tango icons are my fav..
Cool compilation buddy
WOW so many icons to choose from!
Great compilations
Awesome list.
Great list, bookmarked. I was aware of 1 or 2. Definately useful in developing websites with look and feel of web2.0.
I found this post via dailyblogtips…
Bookmarked! Great collection. I like the Crystal Clear Icons.
This looks fun!
Stumbled! 
I love icons. Thanks for this collection. Stumbled.
nice…thank you very much for posting these helpful info on icons and where to find them…
saves us a lot of time…
great post bookmarked.
Excellent post! thanks for sharing.