For S&P: Invesco S&P 500 UCITS ETF Dist ISIN IE00BYML9W36, Ticker SPXD
cheapest and almost best return tracking the SnP 500
For Developed World: HSBC MSCI World UCITS ETF USD ISIN IE00B4X9L533, Ticker HMWO
best performing and one of the cheapest developed world trackers
For World Emerging Markets: ComStage MSCI Emerging Markets UCITS ETF ISIN LU0635178014, Ticker E127
cheapest and almost best performing Emerging Market Tracker
For All World Index: Lyxor MSCI All Country World UCITS ETF - Acc (USD) ISIN LU1829220133, Ticker ACWL
And SPDR MSCI ACWI UCITS ETF ISIN IE00B44Z5B48, Ticker ACWI
Cheapest and best performing MSCI All World tracking ETFs
I feel these are vitally important ETFs for people that want to diversify their portfolio with buy and hold long term strategies, as you would expect to be your core market in your ISA product