Made this little jobby last night after stumbling across this: https://github.com/paulirish/git-open which is also awesome.
Launch the homepage: gem home gem-name
View Issue tracker: gem issues gem-name
View Documentation: gem docs gem-name
It tries to do some clever stuff like falling back to github url's if the gem creator didn't add explicit links. Falls back to rubydocs if there are no links and the gem isn't hosted on github.
To Install: gem install gem-home