Lately, I've been really paying attention to how much functionality you can reuse for free from major players. For example, you can check out the various Google APIs (http://code.google.com/)and the Yahoo! User Interface Library (http://developer.yahoo.com/yui/). These libraries are free, released via Open Source licenses, and offer ridiculous amounts of functionality.
As a developer, I love the idea of being able to leverage the work of other people. Most of the time, this is hard to do because so much of the code that everyone else writes is crap. ;-) But seriously, there is even a name for this, we call it Not Invented Here (NIH). The premise being most developers like to know exactly what their code is going to do, so using someone else's code can be hard.
In the case of the big boys like Yahoo! and Google, it becomes a lot easier to trust that the code is going to deliver expected results and not be malicious or buggy. After all, when it is provided (and used) by a company with billions of dollars of online reputation to uphold, you can pretty much bet they've tested it.
Which isn't to say that just because they are all that, you don't need your own bag of chips, they have their issues too. Dependency and version issues, occasional bugs, and warped programming models are abundant. But in the end, you are definitely getting your moneys worth.
The chart at the top of this post is generated using the super cool (and free!) Google Chart API which means I won't be paying for Dundas or ChartFX licenses again. You can find the details at http://code.google.com/apis/chart/.