Vinay NP
Vinay NP reviewedRegExr 2.0Online tool to learn, build, & test Regular Expressions
 RecommendedPros: 

UI | Help text on hover | Community contributed expressions

Cons: 

RegExr can be ade even more awesome with a day mode and a theme switcher

This is one of the best tools to hand hold you in the painful process of debugging regular expressions!!