Hi kai, nice to see you. Hey, tarra! You were supposed to wait to post till I was done typing! 
This is a stringently edited set of suggestions for tarra. I have lots and lots and lots more, but I’ve tried to restrain myself.
If you like begonias, you may want to branch out and go beyond regular (wax) begonias. See if you can find either Dragonwing or Angelwing begonias. You can look in any OK nursery. But you might also find them in a houseplant section of any store. I bought 6 extremely nice begonias at Marc’s on Saturday (it’s kind of a discount grocery store with other stuff thrown in). They look like they might be Rex begonias (they were labeled “foliage” :rolleyes: ). I just know they’re pretty. I planted a dark red one with a lime green sweet potato vine and another plant I’m forgetting now. Your pots are probably too small for sweet potato vine, but you could use something like helichrysum/dichondra Silver Falls (scroll down toward the bottom of the page). You could combine this with wax begonias too. There are helichrysums in light green as well.
When we plant containers at the park, we generally go for a pointy/upright plant, a roundy-moundy one and a trailey one (yes, those are the technical terms).
I’ve taken to scouring houseplant sections of big box stores for plants, especially for the pointy ones. I’ve used several small palms. They have prettier leaves than the usual dracaena spikes that you see everywhere. I have friends who have found Alocasia amazonica “African mask” in the houseplant section of Lowe’s. (Much cheaper than at the swanky nursery.)
Other plants that I really like (that will do well in shade/part shade/part sun: Persian shield (strobilanthes) (looks really nice combined with something white (bacopa or Euphorbia “Diamond Frost” or white impatiens. Since your containers are relatively small, I’d put Persian shield in one and impatiens (or some other white plant) in another. Persian shield can get very large, but you can always prune it if it gets too big for your taste.
I love love love that Diamond Frost I linked to above. It’s a really nice filler and “blooms” all season (they’re really bracts and not blossoms). This is the third year I’ve used it and it always makes everything it’s planted with look nicer. It’s getting to be more commonly available, but I haven’t seen it at a big box store yet.
Plectranthus “Nico” is really nice and easy to take care of too. Use it like Persian Shield. You can use coleus in a similar way, too. Don’t make that “I hate coleus” face. There are a lot of varieties that are very pretty. I’ve even found some nice, good quality ones at Home Depot.
This year, I also planted this Osteospermum. I have it in a partly sunny location. We’ll see how it does. (The blossoms were just too cool to miss.)
Anyway: for variety, I’d try some type of filler either in it’s own pot or with whatever main plant you decide on. I wouldn’t do more than 3 plants per pot (don’t know what you usually do).
Hope some of this is useful. Feel free to ask questions here or via PM. And yes, kai, I’ll post some pics soon.
We now resume our non-gardeny MMP: I’m tired. Maybe I’ll crawl into bed.
GT (sometimes I get a little carried away by plants; pretend they’re kittens)
Sorry works sucked today.
And now I’ve got options galore!! Most of my previous purchases have indeed been either at one of the grocery stores or at Lowes. I loved the selection at Lowes, but it’s hard for me to get there and back; I think I’ll have to cave and shell out for cab fare to do it this time, though. I need a trowel and gloves too as well as a couple of bags of potting soil. I’ll probably do that first thing Saturday morning (hopefully before the crowds get there!!), then I’ll have the weekend to do my potting. Woo hoo!!
