ggplot2 avoid boxes around legend symbols
Solution 1:
You're looking for:
+ opts(legend.key = theme_blank())
You can see lots of examples of all sorts of this stuff in ?opts. I couldn't remember off the top of my head which one it was, so I just tried a few until I got it right.
Note: Since version 0.9.2 opts has been replaced by theme:
+ theme(legend.key = element_blank())