First, it would be helpful to know what zone and/or area you live in- not all herbs grow everywhere.

Most herbs are not noted so much for their blooms as they are for their foliage. But stay away from mint for sure. And tarragon, it can get very invasive.

There are many variegated forms of herbs, like lemon thyme, variegated sweet marjoram, and colored sages like variegated sage, golden sage, and purple sage that are pleasing. Sages can get pretty big and bushy. Lavenders are noted for their blooms and sweet scent, and some of them are fairly small. Depending on where you are, rosemary has pretty flowers, but they can be rather brief. Chamomile has pretty little daisy like flowers, and so does feverfew. Borage has lovely blooms over a longer season. Nasturtiums are pretty and totally edible, but stick with short dwarf kinds rather than vining kinds or your nasts might overwhelm your irises.

If these are bearded Irises their rhizomes need to get sunshine. It wouldn't be a great idea to cover the rhizomes with foliage. I would use herbs which also like lean and sunny soil - which gives you a lot of choice - thyme, sage, oregano, etc. I wouldn't use Borage or trailing Nasturtiums as both produce a lot of vegetation which could cover the rhizomes and possible lead to rot.

It would be useful to know where you are gardening too.

Besides your zone and sun level of the spot (shade, full sun, etc.), do you mean only kitchen use herbs or are you including medicinals and others?

FataMorgana