I plant lilies (all type - oriental, asiatic, trumpets, daylilies) Irises, Salvia, Peonies, Nigella, Veronica, Fox Glove, Tall garden Flox and Millenium delphiniums with my oncebloomers. In fact I also plant many other perrennials as well, just the list will be too long :)There are only few things that I try to avoid like morning glory ,mexican evening primrose, mint, etc.
Olga

Balloon flowers, ornamental grasses, daylilies, coreopsis, heliopsis, that's a start.

It sounds like this might be too formal a layout to be satisfactory with perennials.

It's not really a formal area, but I should have made it clearer that it's a large shrub border backed by a holly hedge. So I was looking for suggestions for the feet of the roses.

Nigella seems like a good idea and would be lovely with the roses and dead by the time the caryopteris blooms.

Anything with the same sun and water requirements as roses. Woody herbs, lavender, scabiosa, germander....in addition to all the above.

I've been trying to tie many of my beds together with liriope as a border and nepeta (catmint) as a filler companion plant. Nepeta hasn't been too aggressive yet, and it does have an exceedingly long bloom period. The blue flowers seem to compliment my roses in any color. I also have lots of clematis going up the climbers.

Robert

Don't forget the verbena.

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I do love blues with my roses - I love nepeta especially. But I think I'd have the same problem as with the geranium. To me, these caryopteris look terrible with other blues. This area faces a porch where I sit all summer and this bothers me.
Maybe I'll move the caryopteris!

Thanks for all the answers
Maureen

I think moving that caryopteris wouldn't be such a bad idea - there's an even nicer one, Caryopteris incana, with much bluer, richer-colored flowers and more compact growth. It's less hardy than Caryopteris x clandonensis, but seeds itself silly and blooms the first year from seed. Its shade of blue would play better with others, and of course, mixing in other colors as "palette cleansers" (pun intended) between disharmonious blues can fix that problem anyway.

They aren't perennials in your zone (or mine either, for that matter), but have you considered Angelonia?

This is Serena Mix
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I have several different caryopteris interplanted with several different yellow roses with blue butterfly bushes as a backdrop (and a few other blues and yellows joining the group). I transition from yellow/blue to pink/purple with dahlias. They produce massive amounts of flowers just when the summer flowers are declining.

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They come in just about every color, and all seem very cheery to me.

Kathy

Digitalis purpurea 'Alba', the white foxgloves, would look beautiful as accents when the roses are blooming. For a low ground cover in front of the roses to replace the geraniums, I'd suggest some Bath's Pink dianthus -- a light pink evergreen variety that will rebloom if you sheer after the flush with the roses, but a light pink will not clash with the caryopteris when it blooms later.

Salvias, I like angelonia also , and jollybee geranium stays shorter than rozanne. If you have the space a smaller variety of acanthus in the background is always nice

One thing I like to do is plant perennials that bloom later in the season when the OB OGRs are done. All by themselves they put on a pretty fine show, but that area can look dull once the show is over. So if you plant flowers that bloom starting in July until frost, you maximize the second show. I try not to waste space in that part of the garden on plants that bloom with the OB OGRs. This approach also gives you a shot at trying an entirely different color scheme, too, if you are tempted. The OB OGRs are all white, pink, dark red, and purple. Later you can switch over to a yellow and blue scheme or an orange, cream and apricot scheme, or whatever intrigues you. By doing this, you get double use of the space.

Rosefolly

I was intrigued by the mention of clematis--I have a huge pink rose, (I don't know what it is & it is actually in my neighbor's yard but has thrown huge long canes mostly into mine) that is beautiful in late May/June, gets a bit of shade in mid summer; it has a rare repeat bloom or two. Would trying to grow clematis in it be harmful to it?

Raee - Your neighbor's rose may be Dr. Walter van Fleet. Unlike New Dawn, it sometimes has a rare solitary bloom or two late in the season, but gorgeous in May/June. Best, Nick