EDITED Wed., 11-4-09: Treefolks called and confirmed what Caroline and Pam suspected: they're both Mexican Plum trees!
While I was out voting today, the people from Treefolks' Neighborwoods free tree program delivered our two "small stature" trees. Unfortunately, they left no identification on the trees. (I've left them a phone message.)
The choices (none of which I have any experience) were American Smoketree, Flameleaf Sumac, Mexican Plum, and Texas Mountain Laurel. I'm looking on the Lady Bird Wildflower Center database but haven't figured them out yet. Does someone recognize these?