Nikon users can shoot just about any Nikkor lens made in the last 30 years, and many are great performers on the Nikon D3 and D700 (in particular with those bodies). And since Canon users can use Nikon lenses with an adapter, the range of optics available is huge. Canon users can also use optics from Leica and Olympus with adapters.
Why shoot older lenses which might test as inferior to newer, “better” lenses like Nikon’s spectacular 14-24/2.8 and 24-70/2.8? Well, every lens has a personality; this includes color rendition and saturation, macro and micro contrast, bokeh (out of focus rendering), field curvature, spherical aberration and other optical characteristics that might not test well “by the numbers”, but might be just the “look” to achieve an artistic goal. (My lens testing always evaluates contrast and resolution as a baseline, but goes much farther afield to find the qualities produced in real images).
A great example of this is the classic and highly sought-after NOCT-Nikkor 58mm f/1.2, now selling used near the US$2500 mark. On the test bench it looks like a “dog”, (and it’s lousy for astrophotography), yet real images made with it are unlike those from just about any other lens (I’ve used 5 samples of the NOCT-Nikkor). So if you have old lenses sitting around, shoot them to see how they perform, but not as to perfect resolution and contrast on a flat field, but whether they render in an interesting way. I sold my NOCT-Nikkor in 2007, a mistake in retrospect, as they are increasingly hard to find.
If you do not have older lenses but want something different for your work, look into the Zeiss ZF line and/or Voigtlander line (in addition to older Nikkors, etc). Many of the Zeiss ZF lenses offer the unusual combination of superb resolution and contrast combined with great “personality”—that’s why the majority of my work is done with them.