1.  I would recommend that (complex-generator) return first

(define special-reals
   '(0 -0 +1 -1 +0. -0. 1. -1. +inf.0 -inf.0 +nan.0 -nan.0))

(apply append
        (map (lambda (first)
               (map (lambda (second)
                      (make-rectangular first second))
                    special-reals))
             special-reals))

as much as possible.  Gambit doesn't have -0, -nan.0; some schemes don't
have mixed exactness.

2.  I'd recommend that (exact-complex-generator) return first

(define special-exact-reals
'(+0 -0 +1 -1))

(apply append
        (map (lambda (first)
               (map (lambda (second)
                      (make-rectangular first second))
                    special-exact-reals))
             special-exact-reals))

which in Gambit is

(0 0 +i -i 0 0 +i -i 1 1 1+i 1-i -1 -1 -1+i -1-i)

3.  Should

(exact-generator) be renamed to (exact-real-generator), and
(inexact-generator) be renamed to (inexact-real-generator)?

4.  Do you mean (number-generator) to be (real-number-generator)?  I
guess I don't really see the difference between

(compex-generator) and (number-generator) (unless you support
quaternions or something like that).

That's enough for now.