I've thought of a few more suggestions:

Silk Tree (Albizia julibrissin) - nice foliage, beautiful flowers and quite hardy, they don't need too much water.

Orchid Tree (Bauhinia variegata) - same as above.

Manchurian Pear (Pyrus ussuriensis) - nice autumn colour, hardy.

Robinia (Robinia pseudoacacia) - very hardy, nice autumn colour, does tend to sucker though so can be a bit weedy.

Look 'em up and see what you think.

HTH