Search on "planting for bees". This has been discussed MANY times.
Here's one of the longer discussions:
http://www.beesource.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=2;t=000500#000000
Here's one of the longer discussions:
http://www.beesource.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=2;t=000500#000000