It's a Harlequin Bug, Murgantia histrionica. Beautiful.
Renee

Here is a link that might be useful: Harlequin Bug

He's not a gentleman, though.

Here is a link that might be useful: Pest info

and info from Univ CA
http://www.ipm.ucdavis.edu/PMG/GARDEN/VEGES/PESTS/harlequinbug.html

Here is a link that might be useful: Harlequin bug - Murgantia histrionica

Well, he can have the radishes! The tomatoes (his back-up dinner) are so big I doubt he'll do much damage.

Thanks for the answer, guys!

As long as he is not joined by forty of his buddies many of which are bound to be female, he will not do too much damage. I would definitely squish him anyway. I had an infestation of green shield-backed bugs (very similar) on my tomatoes and they devastated the crop, and it took me two years to get them under control through hand-squishing. Ick.

I saw two ginormous praying mantises in the same raised bed this morning...they may do the squishing for me!