Frogs are generally lunar symbols as well as water symbols.  they can represent the Yin side of Yin Yang .  They can also symbolize fertility and resurrection (frogs have been known to hibernate for years after getting trapped in a construction project, only to revive after being freed).  It can be a symbol of life, but usually material life, not spiritual. 
In Christianity, a frog can represent the positive idea of resurrection, but more often represents negatives like evil, sin, and heretics.  Also, one who seeks material pleasures,   A frog in a well symbolizes a person of limited vision or one who lacks understanding, especially understanding of spiritual matters. 
In ancient Egypt, the green frog represented new life and abundance.  Also strength born out of weakness. 
In ancient Greece and Rome, the frog was a symbol of Aphrodite and represented fertility and harmony between lovers.
In some parts of the world, the frog is a symbol of good luck.  A frog pendant or totem is used for protection.  The frogs transformation from a tadpole to an adult is symbolic of awakening creativity.  The Irish consider frogs close relative of the magical leprechauns. 
The toad, which I only recently learned is actually a type of frog, symbolizes much the same, but more often the negative aspects.  They represent the powers of darkness, evil and sin.  In China, a three-legged toad is the symbol of the god of wealth so is symbolic of abundance.

Note: frog drawing from http://allaboutfrogs.org/