All five of us here are kind of smitten with this smoothie. It is so refreshing, and the lime juice creates an almost fizzy feeling to it. The ingredient amounts are very flexible, of course, so feel free to play around with them to suit your tastes. I love using home-canned pineapple, but canned pineapple from the store would work as well. I don't suggest using fresh pineapple, as the taste is more acidic and it has a tendency to overpower the other flavors.
Also, I like to freeze my bananas when they're slightly underripe. I just peel a bunch and put them in a gallon ziploc bag for use in smoothies. If the peel has brown spots at all, the banana taste is too much for me, so I like to freeze them when they are still tinged with green.
2 cups frozen strawberries
1 cup canned pineapple, drained
1 frozen banana, cut into chunks
1/2-1 cup milk (start with 1/2 cup and increase as needed)
juice from 5-6 medium limes
1/4 cup sugar
Combine ingredients in blender. If your blender isn't very powerful, let the fruit sit for 5-10 minutes to soften up a bit before blending. Blend until smooth, adding milk, lime juice, and sugar as needed. (And don't be shy with the limes! This tastes best with a pretty good lime flavor, so if your limes aren't very juicy you may need to add more.) Enjoy!