Charting services allow users to look at charts showing the price (and other measures) of a stock or mutual fund over time. The data for the charts comes from the stock exchange where the issue is listed, and vendors buy the data stream and package it. THere isn't any difference in the data that is displayed on two different charting services.
The difference in the charting services has to do with how the financial data is displayed, how the charts are formatted, and the additional data points (volume, trend analysis, comparison to indices, etc.) that can be displayed. The main point is that you should find a charting service that gives you the information you need in the format you need and stick with it.
In addition to the charting services listed below, many of the other sites listed above (Dailystocks, Morningstar, Google, etc.) also have charting capabilities on their sites.