tl;dr: free seeds! Scroll to the end. As of November, I still have plenty available.
I grow herbs and a few vegetables in a small garden patch every year. I've never had much success with flowers, except for sunflowers and marigolds. Both are self-sufficient and add cheer and color to even the smallest garden space.
I've only used them as a companion plant for tomatoes, but they're also said to do well growing alongside peppers, potatoes, and eggplant.
Per Wikipedia, the genus Tagetes is what I'm familiar with, though I've no idea what species I've got. They produce small, densely petaled flowers ranging from sunny yellow to rust orange: photo here; excuse the weeds.
Aside from being pretty, they have the added benefit of being useful: they keep (some) aphids and other common pests away, apparently through their pungent, though not unpleasant, scent. I've noticed a huge difference in aphid population in years when I haven't had marigolds around. This may not ward off every aphid, but it's a cheap, pesticide-free, round-the clock advantage.
Here's how terrifically low-maintenance these are, at least in my latitude: you plant them and they grow. Even better, though they do die off at the end of the season, they automatically re-seed the ground for next year's flowers, which will start growing on their own as soon as they're ready.
I've found many flowers to be fussy about soil and moisture conditions, but marigolds are troopers who make the best of it, even squeezed into odd garden spots. Mine have done equally well in sun and shade, and don't seem to notice when I totally fail to water them. I don't know how it's possible. And - granted, I live in the south - they keep producing blooms from early summer up through the first frost, at least. For me, that could mean Christmas.
The plants usually only grow to be about a foot tall - occasionally 18" or so. For this reason they can be scattered throughout a garden without fear of them causing too much shade for other plants, or hogging the water and nutrient resources.
Anyway, the whole reason I've written this up is to offer you guys some seeds from whatever hardy variety I've lucked into. Last year's crop yielded more seeds than I can possibly use, and they won't last forever. I feel it's reasonable to limit this offer to people who have at least one writeup under their belts, but other than that, no strings attached, just drop me a line if you'd like to try growing these, and I'll be happy to mail you a packet.