Stephen Celis provided a slick bash-method for quickly opening and browsing RDocs, over at his blog. I have merely ported the function to zsh. As a slight modification, $BROWSER and $BROWSER_OPTIONS are used instead of just open, so it works cross platform. The code:
gemdoc() {
local gemdir=`gem env gemdir`
$BROWSER $BROWSER_OPTIONS $gemdir/doc/`ls $gemdir/doc/ | grep $1 | sort | tail -1`/rdoc/index.html
}
_gemdoc() {
compadd $(ls `gem env gemdir`/doc)
}
compdef _gemdoc gemdoc