Wild guess - Cornelian Cherry (Cornus mas)? It's a dogwood relative, so look for opposite leaves. The main argument against that ID is that it's pretty late for C. mas to be blooming.

Here is a link that might be useful: Cornus mas pics (scroll down)

Forsythia?

Is it sweet-scented -- maybe Clove Currant Ribes odorata?

LynnT

Thank you Lynn! Clove Currant it is! I looked it up and that's exactly what it is. I'll include a link to the page I saw it on if anyone is interested - just choose Common Name and type in Golden Currant. Thanks to Gardenpaws and Blueheron for your suggestions too.

Here is a link that might be useful: Golden Currant - Ribes aureum Pursh

Would you possibly feel like sharing cuttings (or seeds in season), if the plant is at your house? I'd love to try it, both for the hummers, and because that species is also apparently the preferred understock for tree-form currants and gooseberries..