Attracting bees to a small garden

I have a fairly small back garden — probably about 30 square metres — but I'd really love to do my bit for the bees this year. I want to plant things that will actually make a difference rather than just look pretty.
What are the best bee-friendly plants for a small space? I've got a couple of pots on the patio as well as a small border, so any suggestions for both would be great.