I've found that Borage is great to repel hornworms from tomatoes. I have one plot up by the chimney from the old house that always used to get lots of hornworms, to the point where they'd eat most of the entire tomato plants. I actually quit planting tomatoes up that way for a few years. I get a few hornworm problems in the garden bed down by the driveway, as well.
Last year, I mentioned this to one of the "old timers" selling some interesting heirloom tomato plants at the local farmers' market. He recommended borage as a border and companion to repel or even kill off the hornworms. I tried this last year with some of my "extra/leftover" tomato starts. I got a couple packets of borage seeds, and planted about every 1.5 to 2 feet around the border, and mixed a few in with the tomatoes. This was up where I stopped growing tomatoes because of the hornworms wiping them out. I didn't have a single hornworm all last summer in those tomatoes. I'm not sure if borage repels the hornworms, or one "old timer" told me that the hornworms eat the borage and it kills them. Whatever the mechanism, borage + tomato plants works well to repel/kill off the hornworms.
Also, a word about nasturtiums and aphids. Nasturtiums don't repel aphids, they attract aphids. Not to the level where they attract aphids to your garden where you didn't have them before. Just attractive enough that if you have aphids in your garden, plant some 'sacrificial' nasturtiums, and all the aphids will go to the nasturtiums and leave your other plants alone.
