The name Caleb comes from the Biblical story of the Israelites sending spies into Zion. Caleb was one of the 12 spies sent by Moses, and one of two who returned to Moses with the news that God would deliver the land to Moses and to the Israelites. The name, according to most interpretations, means simply Dog. According to other interpretations, the name is symbolic, meaning Loyal (to God).
Currently the 31st most popular boys' name in the US, Caleb is actually gaining in popularity. Perhaps it's due to its popular shortened versions (especially Cale and Cal), and perhaps it's due to the rise in demand for what many consider a very masculine and serious name that doesn't sound too popular.
2010 Update:
Perhaps the name has reached its peak and it's downhill from now on. It is now at number 33.
