This is really nice, but I've always enjoyed RegexPal [1]. It's got a nice clean simple UI, displays results immediately and allows me to prototype regular expressions very quickly. Use it almost every time I wrote a regex.
The problem is, regex flavors differ, and RegexPal uses JavaScript - whose regex flavor is really limited compared to most others (including Python). You should always try to find a tool that uses the regex flavor you are targeting.
Perhaps related -- some genius has registered http://strftime.org and lists out python strftime formatting directives. Very handy as a quick reference.
[+] [-] maxerickson|12 years ago|reply
http://hg.python.org/cpython/log/979eb1bbf6e6/Tools/scripts/...
[+] [-] tsergiu|12 years ago|reply
[+] [-] gnosis|12 years ago|reply
Emacs has M-x regexp-builder
[+] [-] whalesalad|12 years ago|reply
[+] [-] p99tourism|12 years ago|reply
[1] http://regexpal.com/
[+] [-] mbue|12 years ago|reply
[+] [-] thwarted|12 years ago|reply
[+] [-] dpmehta02|12 years ago|reply
[+] [-] gpsarakis|12 years ago|reply
[+] [-] unknown|12 years ago|reply
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[+] [-] markdown|12 years ago|reply
[+] [-] orta|12 years ago|reply
[+] [-] jessedhillon|12 years ago|reply
[+] [-] marios|12 years ago|reply
[+] [-] unknown|12 years ago|reply
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[+] [-] jfb|12 years ago|reply