How much sun does this area get? How big is the planting bed? Do you want season long color? what color, evergreen, short, tall, shrub, perennial, annual, variety of plants or just 1 or 2? FWIW I have a bridal wreath spirea in the south west corner of my house that is in a partly shady spot so I have part shade plants nearby (Brunnera, creeping phlox, tulips, hostas, siberean iris)

Ohhh, there are so many choices! Are you looking for things that will bloom other than in springtime? All of those listed above bloom pretty early. I have the yellow (and red and lavender Epimedium) and it's new leaves emerge bronzy like the photo above, so I don't think it has to be E. rubrum I have hellebores, solomon's seal, false solomon's seal, fairy bells, dicentras ( the little ones, pink and white), lots of early bulbs, primulas, dwarf hostas- I have a tiny 2" high one that gets deep purple flowers, Paris, spotted hardy orchid- (Dactylorhiza maculata), double bloodroot (I love the flowers, and they last a lot longer than the singles), corydalises- Corydalis Flexuosa Purple Leaf, Corydalis ochroleuca (white flowers-neat habit, and will bloom for months!), and one that I forget the name, but the leaves look like a fern and it gets yellow flowers (not lutea), arum italicum, Hakonechloa (I have several varieties), oh and Himilayan blue poppy, ummm can't think of any more off the top of my head... Heucheras, Lime Ricky really stands out in the shade, as does Stoplight. Oh, and shooting stars, camassia, anemone nemerosa (the double white again lasts the longest)...depending on the amount of light- Astrantias, ajugas, one of my favorites is A. Metallica crispa- it's tiny and well-behaved.

I grow marigolds on the edges of my lasagna beds, but it's more of a pretty factor than a companion factor. And with this years bed rotation, the marigolds are on the edges of pepper, squash, and bean beds, and not along the tomato beds at all, lol. And I thickly direct sow marigold seed too- that way it's a nice bushy border and if/when they get bug-tacular I can just pull those plants if needed. This year it's carrots and leafy greens edging the tomato beds- but that's more of a got that little space left over I can cram them into rather than companionship. But hey, if it helps, why not? I've never been sure how basil is supposed to improve tomatoes either- I always figured it was kind of an old wives tale because tomatoes and basil are so often companioned in cooking rather than the growing aspect of it. I would never grow garlic in my tomato bed- my garlic gets it's own beds, and honestly is one of the only beds that is perfectly picked clean of anything that could compete with the garlic. Garlic might be good for tomatoes, but I wouldn't want to chance tomatoes out competing my garlic. Borage gets it's own growing space too, because it has it's own application, and I don't want it competed with. I grow calendula aside too for the same reason. My sage is in the herb garden, and I don't grow chives because I have large swaths of my lawn that are thick with wild chives so I don't need to grow any. Nasturtiums can be a great companion plant as far as I'm concerned- but as a companion plant only as a trap plant that I'm willing to sacrifice. I had a nasty aphid infestation last year, and the nasts trapped almost all of them- and when a bit of the plant got infested, I promptly cut it off and drowned it. I grew them next to peppers and squash last year, and they didn't get a single aphid. I wouldn't rely on nasts as a companion to just let sit and do whatever. But then I have the tendency to grow hedgerows of nasts because I use them a lot for various eating too, so I can use them as sacrificial companions and eating plants.

ahappycamper - I don't 'throw' any of my vegetables. Brassicas are grown about 2 feet apart. Lettuce about 6 inches. These are all planted out as transplants, not seed. I grow the plants from seed myself but not in situ. Despite what others say about deep and shallow rooting plants, intercropping of salad and brassicas works. It is tried and tested and a common practice over here. The salad is all harvested in the summer by the time the brassicas are ready in the winter. Here's the link again The picture shows Chard and Red Russian kale on my allotment. It wasn't taken to show intercropping hence you can't see the rows in total.