Yes, if you're maxing out your workplace retirement account an IRA is a logical next step. You might prefer to contribute to traditional based on your tax bracket, but if Roth is your only option because of your income then that's better than nothing!
As to what you should invest in, I recommend writing up an "investment policy statement" (search for that term elsewhere on the forum for more info) that basically says how much of your investments you want to have in stocks, bonds, US, international, other asset classes and why. Once you've done that, the choice for how to invest the next dollar should be pretty obvious: look at where your current investments are out of whack with what your ideal asset allocation is, and put more into whatever is falling behind.
