Unlike cool-season grasses, warm-season sorts go partially to completely dormant during winter (depending on how cold the weather gets) whether water is available or not. The group includes common Bermuda and hybrid Bermuda, zoysia, St. Augustine, bahia, centipede, and buffalo grasses. All grow most vigorously during hot weather, and most are grown in the warm climates of the South and Southeast, as well as in some parts of the Southwest and Far West. Buffalo grass has so far been most widely used in Texas and parts of the Great Plains states.
Common and hybrid Bermuda are among the most popular warm-season grasses. Both are relatively drought tolerant and very resistant to wear and tear. Hybrid Bermuda is finer textured than common Bermuda and doesn't turn brown in winter as readily.
Perhaps the toughest and most drought tolerant of all the warm-season grasses is zoysia. It's also one of the most attractive, but it tends to go dormant sooner and stay dormant longer than the others.
Note that both Bermuda and zoysia are so tough and vigorous that it's hard to eliminate them should you ever want to replace them with a different type of grass. Both are invasive, as well: they'll travel into other parts of the garden via underground or aboveground runners. Be sure to monitor them and remove stray growth regularly.
St. Augustine is another tough (and invasive) variety; it tolerates shade and seaside conditions. It's moderately drought tolerant but looks quite shabby during winter.
Drought-tolerant bahia grass is a good choice where soil is sandy or acid; it's popular in Florida. Centipede grass is widely used throughout the South in regions where soil is infertile, acid, or both. It needs regular water and doesn't take heavy foot traffic.
Gaining in popularity is our native buffalo grass. It forms the sort of even-looking, "classic" lawn we associate with cool-season grasses, but it survives intense summer heat and retains its color for much of the summer with little additional water (though it does tend to turn brown as summer draws to a close). It thrives in many parts of the country, even in areas where cool-season grasses are grown--but gardeners in those regions prefer grasses that stay green year-round. However, new hybrids are being developed that hold their green color longer, giving buffalo grass a wider appeal.
One drawback to warm-season grasses is that they're difficult to establish from seed (with the exception of bahia and centipede grass) and must be started from sod, plugs, or sprigs. Of those started from plugs or sprigs, St. Augustine and Bermuda initially spread and fill in faster than the others.