If you are in this thread then chances are you are interested in investing/trading. I have seen lot of visitors in Sajha looking for info to get into investment world as I used to be one of them. Having been travelled the same road I would like to offer my 2 cents here for starters. I would say Yahoo finance, Google finance, cnbc.com would be good place to start. Pick some companies you like and follow them for a while. Look at their historical performance, estimates, P/E ratios, earnings, future plans and compare them to overall industry. I would recommend to start with large cap companies Example Google, Apple, IBM, Exxon Mobile, MacDonald, Pepsi, General Electric coz they are much safer in the volatile market like this. Once you get more comfortable you can move into start ups, small caps and emerging markets where risk are high but reward could be handsome as well. Next step i would recommend is to open an account with discount online brokerage firm such as scottrade.com, optionhouse.com, etrade.com. Check out OPTIONHOUSE.COM, here you can try with virtual money first. Over there try differnt type of sell and buy orders (which I highly recommend, coz I personally have screwed up good chunk of profit when i put wrong kind of sell order) once you feel comfortable, know the basic rules of investing and you think what you are doing you can start investing.
Oh yea! Before investing your real money analyze yourself. Do you want to be a trader or an investor? Personally I like investing than trading, but if opportunity presents itself I am ready to jump in and trade as well. 
Hope this helps. Happy investing fellas :)