For a hitch
http://www.minidomore.com/
They've also got a bike carrier.
But, what I use is the minidomore hitch plus this
http://www.sportsrig.com/
I love my trailer. I use it mostly for bikes, but I've also loaded it up for trips to recycling and such.
No inexpensive options I'm familiar with!
If you want to investigate more, you might try out the MINI forum.
http://www.northamericanmotoring.com/
...and you just got the best car in the world! I love my MINI (clubbie, traded in my Cooper for a little more room).