Google finance is a simple app that gives you your market overviews, news, and you can set up a portfolio of stocks to keep an eye on. Depending on if you have a brokerage account look for yours, I have Schwab and love the app. The CNBC app is also decent, last i used it though it felt a bit cluttered to me, worth a shot though.
One of the best Android stock apps is the My Stock Genie by MoneyWorks4me.com. all stocks have been colour coded according to their fundamental strength and you can get the ideal buy and sell prices also. Also it lets you set triggers on stocks in your boughtlist and the alerts are sent through SMS.