Mine

Match ==something==

^==([^=]+)==
[size=4]\1[/size]

^===([^=]+)===
[size=3]\1[/size]

^====([^=]+)====
[b]\1[/b]

^=====([^=]+)=====
[size=1][b]\1[/b][/size]

^======([^=]+)======
[size=1][b]\1[/b][/size]



URLs
order important:

\[\[([^\|]+)\|([^\]]+)\]\]
[url=http://wiki.what.cd/index.php/\1]\2[/url]


\[([^ ]+) ([^\]]+)\]
[url=\1]\2[/url]




Bold and Italics

Order important:

first:
'''([^']+)'''
[b]\1[/b]

then:
''([^']+)''
[i]\1[/i]