\eqref
Another case where one only wants to change the information associated
with the label category is to change the macro which is used for
referencing the label. When working with the AMS-LaTeX, you might
prefer \eqref
for doing equation references. Here is how to
do this:
(setq reftex-label-alist '((nil ?e nil "~\\eqref{%s}" nil nil)))
RefTeX has also a predefined symbol for this special purpose. The following is equivalent to the line above.
(setq reftex-label-alist '(AMSTeX))
Note that this is automatically done by the amsmath.el style file of AUCTeX (see Style Files); so if you use AUCTeX, this configuration will not be necessary.