What about Zonal Geraniums? Nasturtium?
Am trying Melampodium this year...it appears to have nice bright green leaves in the pics people have posted.

I think the foliage of Cosmic Orange Cosmo is nice.... Looks good near silver foliage and they only get about 15" tall and have good form. The silver foliaged one next to it is Venidium 'Jaffa Ice' who flowering stems are pretty tall and flowers like Gazania only open on sunny days; closing at night.
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Triple Purple Datura has nice dark burgundy foliage and stems...
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Profusion Zinnia...
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....and of course I always think Sunflowers have awesome foliage!
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The leaves of nicotianas look big and lush near the ground. I grew N. alata with nothing in front of them and the leaves looked attractive from several feet away.

It does't flower or maybe it just didn't last long enough in my climate to flower but the foliage of burning bush (kochia) is really nice and feathery. It turns red in the late summer/early fall. A nice filler for bouqets too.

I 2nd Nicotiana alata as well as long as they don't get a bunch of bugs stuck or animal fur on the sticky leaves :D

vera, what's the purple leaved plant shown in your bottom picture? An amaranthus or a purple basil maybe?

I underplanted my roses with basil this year. I was really happy with the contrast of the bright green basil leaves and the small leafed box which borders this bed. The basil flowers are insignificant but the bees were crazy for them! I took this photo at about 7.30am so I guess the bees are still asleep...

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I like marigold foliage too.

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Begonias have lovely foliage and flowers:

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These aren't any of the begonias with showy foliage - spotted or streaks or ruffles...

I also think when you have a nice canopy of impatiens the foliage is lovely (with the flowers). But that's me -

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I have recently seen a few geranium varieties with beautiful foliage. Sadly, I bought some and never was able to bring them to flower so I can't speak to what the flowers looked like. The only geraniums I have ever failed at but will likely try again because they were really pretty and I brought them in as indoor plants in winter.