Used Litespeed Bikes
Litespeed is one of the first and definitely most popular titanium bike makers. Founded in 1986 after a family member was injured and took up cycling, Litespeed has grown to be a major American bicycle manufacturer. Used Litespeed bikes are a great value --- though double check the welds. Welding titanium is more difficult than welding steel or aluminum and cracks can develop at the weld.
The company is well known for making titanium frames but they have also branched out into carbon bikes now as well.The benefits of titanium as a frame material is another story, but there are many:
lighter than steel
no paint necessary
Older titanium Litespeed road bikes are still in high demand and the prices on eBay are still fairly competitive as a result. However, compared with new bikes, getting a used Litespeed titanium bike is a great value.
Litespeed has been making road and mountain bikes for a long time and consistently. However, they have not spent considerable time in the triathlon and cyclocross bike markets. Litespeed has made a triathlon bike called the Blade, which Lance Armstrong rode in the 1999 Tour de France. They have also made a touring bike called the Blue Ridge that many have used for cyclocross (it does have cantilever brakes).
There are other makers of titanium bikes (Merlin, Independent Fabrication, Lynskey, Moots) but the name most synonymous to titanium is Litespeed.