The first stock based ETF which was created in the nineties was the State Street S&P 500 SPDR with the ticker symbol of SPY. This is the most popular ETF.Other popular stock based ETFS are ONEQ (Tracking NASDAQ Composite Index), QQQ (Tracking NASDAQ 100 Index), DIA (Tracking the Dow Jones Industrial Average Index.
There is also MDY (Tracking S&P 400 Mid Cap Index), IJR (Tracking the S&P 600 Small Cap Index).
ACWI (Tracks the MSCI All World Index), EEM (Tracks the iShares Emerging Market Index) and GLD (Tracks Gold Bullion).
On the Bonds side, AGG (Tracks the Barclays Aggregate Bond Index).
For Real Estate assets, IYR is a popular ETF which tracks an index consisting of US Real Estate Development companies.