find index of a stock
Google search does not produce a single website (on first page) that has the information I describe below. So, this would make a great addition to Yahoo - Finance.
Given a ticker symbol, display the Market Index to which that ticker symbol is part of. For example, if I type AAPL, i should get a result back with ( SPX, NDX, DJI, DJA, OEX, S5inft). This is incredibly useful for small cap stocks (like Russell 2000) which are not discussed much on web and hence information is lacking on those ticker symbols. Even finding the index of midcap stocks proved to be more difficult than i expected in a simple web search. So, add this functionality to Yahoo->Finance home page ( even if that happens to be at the bottom of the page). A google search like "Map ticker symbol to stock index" should lead to yahoo finance, with such a functionality because none exists right now in search results.
N S commented
In this regard, to see a website that can give Idea on how to organize this information is
where you can click on the subsection called Index-Component, to find the indices that a ticker belongs to. That is a nice way to present under the ticker symbol page of Yahoo.