Free nifty online utilities

http://ideone.com/
 An online compiler and debugging tool which allows to compile and run code online in more than 40 programming languages.

http://browsershots.org/
Browsershots makes screenshots of your web design in different operating systems and browsers.

http://rubular.com/
A handy way to test regular expressions as you write them.

http://jsfiddle.net/
A html,  css  , javascript play ground. Also supports many frameworks like jquery ,YUI , Prototype etc

http://www.wolframalpha.com/
It's a computational knowledge engine: it generates output by doing computations from its own internal knowledge base, instead of searching the web and returning links.

http://yuml.me/
Create and share simple UML diagrams in your blogs, wikis, forums, bug-trackers and emails.

http://pixlr.com/editor/
An online photo editor.