Problem area -- suggestions?

The far back of our yard has a 6 foot tall stone wall topped by some trees and shrubs (and sort of supported by other trees for that matter). It's fairly shady (the trees dome in the back) but it gets indirect sun as well as a little direct sun in the afternoon. It's a decent little microclime courtesy of the wall and the trees all the way around. We're in Zone 6a.
I'd like to get some flowers growing back there to attract butterflies, bees and other insects. Cash is tight so I figured on getting seeds to sow -- kind of set it up "wildflower style" (although not really wildflowers as the area gets limited sun of course). One area is typically damp but the rest is pretty much your standard-substandard. The trees drop lots of leaves so the soil should be fairly decent.
Any suggestions on some seeds to cast in the area?
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