I lived in Dahab for 2 years. It's not a bad place with a nice relaxed approach to diving - mostly shore based so no running to the jetty a a ridiculous hour. If you're not AOW it's well worth doing. Top sites to take in:
Bells to Blue Hole - Classic Wall dive
Canyon - Lie on your back and look up.
Islands - Awesome Coral formations
Thistlegorm - worth doing if you have time.
You can get away with a 5mm in Winter with a hood. I was doing 100m dives with a 2hour run time in January with a 5mm Fourth Element Proteus wetsuit and toasty warm.
Dive centres - Hilton (if you dive here get some photos by Rich Carey, he's awesome), Sunsplash.
In the evening drink at the Furry Cup in Blue Beach. The Thai restaurant in the bay is good for eating.
None diving - Coloured/White Canyon, St Catherines/Mt. Sinai or quad biking in the desert.
Cheers