There are several especially hardy palms. Windmill palm (Trachycarpus
fortunei), which has a "traditional" palm tree look to it; and
Mediterranean fan palm (Chamaerops humilis), commonly a houseplant; are
typically safe down to 5 degrees (Fahrenheit throughout) and may be the
most ornamental of the lot. Needle palm (Rhapidophyllum hystrix) and
the palmettoes (Sabal minor, Serenoa repens) are still hardier but not
very tree-like.

There was a discussion on rec.gardens of hardy palms that mentioned
quite a few more and some unlikely places to grow palm trees.

If you could count on lows no colder than 20 degrees, you could grow
almost any palm. But around Dallas, I think you have to allow for lows
of 10 (maybe 15 in a favored location) degrees.

--
Chris Green