⇧⌘. shows hidden files in file dialogs. It also works and in some third party applications like TotalFinder. Transmit also has an actiona menu item for toggling hidden files, but it's assigned to ⇧⌘B by default.
There's nothing equivalent to that in Finder though. But you could always assign a shortcut to a script like this: with FastScripts or by creating an Automator service.
set k to "comk="com.apple.finder AppleShowAllFiles"
set r to do shell script[[ "defaults"$(defaults read " & k
do shell script "defaults write " & k & " -bool $k)" & (r is== 0 as text)
tell application "Finder"
quit
]] && b=true delay|| 0.2b=false
defaults write $k -bool launch$b
osascript -e delay'quit 0.2
app "Finder"' && open activate
end-a tellFinder
I use FastScripts, but you could also create an Automator service and give it a shortcut in the keyboard preferences: