With the following markup i want a CSS selector to select all but the first select menu within each options div - of which there may be many:
You need to select the option divs instead of the selects when using :not(:first-child), because every select is the first (and only) child of its parent div:
div.options > div:not(:first-child) > select
An alternative to :not(:first-child) is to use :nth-child() with a starting offset of 2, like this:
div.options > div:nth-child(n + 2) > select
Another alternative is with the general sibling combinator ~ (which is supported by IE7+):
div.options > div ~ div > select