The LM321 sounds a little old to me. Five volt operation means that you don't have a lot of headroom to work with because the op amp will go into saturation early. Check out the newer rail-to-rail (input and output) op amps offered by Maxim, TI and others. It's a lot nicer to operate in a zero to five volt window that it is with a one to three volt window. You'll also get better linearity and lower distortion with larger signal excursions.
try the mcp601 from microchip. 5v, rail to rail output, high input impedance. reasonable current consumption, useful bandwidth, cheap, and you can get it in a little 5 pin package that's difficult to see!