Essential Lens to buy

[daredevil123]

If my budget was unlimited, must-buy lenses would be every lens that has ever been made. For my lens museum. It would take quite a few years, but eventually I'd get pretty close.
Meanwhile, I'm quite satisfied with my 17-85, 50 1.8, 55-250. Planning to get a 30 1.4, for my crop body. (My lens "collection consists of new and used, spent a total of around $850-900. Hope this helps.

If budget is unlimited, just buyout both corporations (nikon and Canon) and you will get access to old and new lenses that are not even available in the market. While you are at it, you can also buyout Hasselblad and Carl Zeiss.