NSE 500 index represents the top 500 companies based on full market capitalization from the eligible universe. It makes up more than 95% of the market capitalization of the stocks listed on NSE and hence best reflect the entire market.
Though it looks like this index provides you with a higher diversification than the Nifty 50, it is not necessarily so. The top ten holdings of NSE 500 make up almost 45% of the index and are similar to the top 10 holdings of the Nifty 50.
Moneyworks4me gives you a comprehensive list of the NSE 500 stocks. You can use the list to effectively sort mid and small cap companies worth investing in. You can look for companies who have done well operationally (higher ROE), or look for companies with decent valuation (P/E, P/BV ratios) and also based on market interest (price changes). You can also use carefully curated Fundamental and Price related parameters to identify companies worth investing in.