I just read an interesting post on Sweating the small stuff by one of the developers of Jottit.

Even though Jotit does not use any fancy Ajax techniques any developer who has done cross browser web application development will understand (and feel the pain) of this quote:

And when you start sweating the small stuff, it's frankly incredible just how much of it there is. Even our trivial site is made up of over two dozen different screens. Each one of those screens has to be designed to look and work just right on a wide variety of browsers, with a wide variety of text in them.

 

In my experience the last 10% of effort  are what make applications a pleasure to use .

Google's finance API looks interesting. Unfortunately it can only be used on Google's properties. I'm sure the providers of this data have some sort of terms of use that prevent Google from making the data available on all sites.

Second, if you're a gadget developer, we've made it a lot easier to make a gadget with market data. We're releasing a gadget API for market data which provides a framework for developers to display stock market information from the American, Nasdaq and New York stock exchanges within a gadget on Google properties. We believe this is the first free gadget API for market data for developers and hope you have fun with it.

API, gadgets, and tabs, oh my!

 

The API really has only has 1 method that gets financial data (as well as an alternative version that gets quotes for an array of stocks).