What is the value of a 1934 A US 500 dollar bill?

As of 02/2012 approximate prices are:

Circulated: $610 to $1200 depending on the bill's condition
Uncirculated: $1400

1934-A was the last series of $500 bills printed. Despite the 1934 series date some were printed as late as the early 1940s.

Serial Numbers
A bill's serial number is a counter and a security feature. In most cases it doesn't affect a bill's value or help to identify it. Some collectors specialize in bills with low serial numbers (e.g. 00000005) or unusual patterns (12344321) so these can bring above-average prices.

DISCLAIMER: The values quoted are market averages as of the date shown, but may be different for an individual bill due to variations in quality and other factors. Also the wholesale (buying) price of a bill will be less than the selling (retail) price. A reputable currency dealer will be able to give a more accurate valuation based on an in-person inspection.