Tired of listening to your neighbors bragging about all their winning S&P 500 stocks? You just got another shot at some of them — thanks to the April sell-off, analysts say.X Seven top S&P 500 stocks up 20% or more this year so far — including Uber Technologies (UBER), Arch Capital (ACGL) and Nvidia (NVDA) — are now at least 11% undervalued, says an Investor's Business Daily analysis of analyst forecast data from S&P Global Market Intelligence and MarketSurge.Why the sudden opportunity? These seven stocks a ...