July was a record-breaking month for Wall Street. The S&P 500 and the Dow Jones touched the 3,000 and 27,000 mark for the first time in history. Optimism surrounding Fed’s rate cut primarily drove the rally. Upbeat oil prices were another factor (read: 4 Reasons That Led Dow Jones to 27,000: ETFs in Focus).Despite a solid jobs report for the month of June and signs of a trade truce between the United States and China, the Fed cut rates by 25 bps at the end of July. Needless to say, global markets were charged-up on cues of more months of cheap money inflow. The upbeat sentiments were sure to leave an impact on the asset flow as well (read: U.S. ETFs Hit $4 Trillion in AUM: 4 Reasons Behind the Boom).After witnessing one of the largest monthly inflows ever in June — $63.8 billion — ETFs raked in $21.7 billion in July, with a year-to-date tally of up to $153.7 billion, per etf.com.S&P 500 RulesAs mentioned above, the top three S&P 500 ETFs — SPDR S&P 500 ETF Trust SPY, iShares Core S&P 500 ETF IVV and Vanguard S&P 500 ETF VOO — raked in about $5.42 billion, $3.28 billion and $1.22 billion in assets, respectively. A record rally in the index drew all investors to these funds (read: S&P 500 Breaks Past 3,000: How to Trade With ETFs).Corporate Bonds: Investors’ Favorite iShares iBoxx USD High Yield Corporate Bond ETF HYG took the third position in asset creation with about $1.85 billion of inflows. A moderately strong corporate America boosted investors’ confidence in this high-yield fund. HYG yields 5.29% annually, which makes it a great candidate amid a low-interest-rate environment.Low-Volatility ETFs in Fine FettleBroader market euphoria couldn’t steal the spotlight from low-volatility ETFs. iShares Edge MSCI Min Vol U.S.A. ETF USMV attracted about $1.55 billion in the month. Trade war tensions, U.S.-Iran geopolitical crisis, lingering risks of an economic slowdown, dovish central banks and low rates made this investing area a winner (read: Top ETF Events of 1H Worth Watching in 2H).Lure for Dividends IntactSPDR S&P Dividend ETF (SDY, which measures the performance of the highest dividend-yielding S&P Composite 1500 Index constituents that have followed a managed-dividends policy of consistently increasingdividends every year for at least 20 consecutive years, has hauled in about $1.27 billion in assets. Quality exposure despite a rocky economic backdrop brought investors to the fund.Small Caps Make a Comeback Apart from the S&P 500, small-cap U.S. ETF iShares Russell 2000 ETF IWM added about $1.41 billion in assets. Upbeat domestic data points veered investors toward this small-cap U.S. equity ETF.Mid Caps Out of Investors’ FavorInvestors dumped mid-cap ETFs like iShares Russell Mid-Cap Growth ETF IWP (exodus of $1.7 billion), iShares Russell Mid-Cap Value ETF IWS (an outflow of $1.25 billion) and iShares Russell Mid-Cap ETF IWR (leakage of $732.3 million).Healthcare Lost AssetsHealth Care Select Sector SPDR Fund (XLV) too shed assets worth 916.9 million in the month.Want key ETF info delivered straight to your inbox?Zacks’ free Fund Newsletter will brief you on top news and analysis, as well as top-performing ETFs, each week. Get it free >>Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report iShares Russell Mid-Cap Value ETF (IWS): ETF Research Reports Vanguard S&P 500 ETF (VOO): ETF Research Reports iShares Russell Mid-Cap Growth ETF (IWP): ETF Research Reports iShares iBoxx $ High Yield Corporate Bond ETF (HYG): ETF Research Reports SPDR S&P Dividend ETF (SDY): ETF Research Reports iShares Russell 2000 ETF (IWM): ETF Research Reports Health Care Select Sector SPDR Fund (XLV): ETF Research Reports iShares Core S&P 500 ETF (IVV): ETF Research Reports iShares Edge MSCI Min Vol USA ETF (USMV): ETF Research Reports SPDR S&P 500 ETF (SPY): ETF Research Reports iShares Russell Mid-Cap ETF (IWR): ETF Research Reports To read this article on Zacks.com click here. Zacks Investment Research Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report