Google has recently announced Google Finance service that competes directly with Yahoo! Finance. Yahoo! Finance has been around for a long time and it is at a much better position then Google Finance. Google Finance certainly is not a weak competitor in the arena. Google Finance has all the basic features a financial website offers you, such as searching symbols in either north America (NASDAQ, NYSE, TSX, etc.) or international (Europe, Hong Kong, etc.) markets.
The company profile is my favourite part of Google Finance. Like Yahoo! Finance, you can select the window size (zoom) of the chart you want to view. You will see flags on the chart which associates with the price and news at that particular time. Unlike Yahoo! Finance, you can also drag the chart and see previous price and news. It also has information of related companies (a.k.a competitors) and blog post of the company you are currently researching. In my opinion, it is much user friendly than Yahoo! Finance.
Google Finance is still lack of features in their portfolio. First, Google Finance does not allow you to add symbol outside US market yet. If you type in ATY.TO, Google Finance says "We will support international symbols soon" So we will see. Second, Google Finance does not allow you to compare performance between different symbols (say, ATY.TO vs NVDA) which keeps me away from using it.
I am very impressed by what Google Finance offers and their interface is the best I have seen by far comparing to Yahoo! Finance and other financial website. It is a bit too much to ask for now since Google Finance is still in beta phase. I believe we will see lot of improvements soon.