With MSP as your base, you're really only limited by your stamina and your back. 19's suggestions are all great, expect maybe for EZE, but then again he is only 19 and listens to that....."music" (oh is he going to get me for that one )
My suggestions
limit yourself to nonstops. I know it's tempting to chance a connection, but if you really only have 24 hours, don't gamble.
Now I usually limit my day trips to 5+ hours of flight time, any more and you run the risk of spending more time in the airport and in the air than at your destination; of course if you don't mind dragging around the next day ...go for it.
Any place on the west coast would make a good day trip. You could spend your day at Universal Studios or maybe Sea World San Diego.
So grab the credit cards and your travel pillow and get going.