Is there any package to change the math font (amsmath Computer Modern) to match the Helvetica font I am using as default in my document (
(In the same way as
mathpazo for Palatino math)
MicroPress has designed the HV Math fonts for which there's also LaTeX support via the hvmath package. Note that the Type 1 version of HV Math is commercial, but there's a free bitmapped version with a resolution of 300 dpi.
EDIT: As Herbert pointed out, the commercial Type 1 version isn't available anymore.