A while back, I discovered the magical .irbrc. If you scroll down to the comments, Arthur and I left a tip on how to view arbitrary script/console output in Textmate. It's really amazing for XML or big chunks of output. Other useful irb links after the fold.
Stephen Cells mentioned the utilitybelt ngem. It might be overkill, but I'll probably pick through for a few good bits.
I added another snippet to my .irbrc for copying stuff to the clipboard on OS X.
class Object
def pbcopy(string)
IO.popen('pbcopy', 'w') { |f| f.puts(string) }
nil
end
end