Personally, I have a self-directed Davy Select PRSA account (0.75% AMC). Using that pension account, one can invest in (among other things) third-party ETFs with various different investments and fees. There's a 0.07% AMC ETF that tracks the S&P, for example. The one I've invested in is denominated in EUR, but I'm pretty sure there was one which is USD-denominated as well.
There may be better options out there, but I'm not aware of any myself.