I've come across a couple of free controls for .NET recently which look pretty cool.
DevExpress - I've always loved DevExpress. Their Delphi controls rocked (and probably still do), their .NET controls rock and their pricing has always been pretty reasonable ($2000* for every .NET control they produce for a year). Now you can get some of them for free. The download is a bit large since it includes trial versions of everything they do but some of them look pretty useful. I haven't looked too closely but from a cursory look it seems like the ASP.NET controls are more useful than the WinForms controls, which are mostly just some edit controls.
Chart control - Microsoft bought the Dundas chart controls and now you can use the Microsoft updated versions in your ASP.NET and WinForms applications for free. I assume at some point these will get rolled into the .NET Framework meaning it will be possible to add charting to apps with no extra installation woes to worry about. It will be interesting to see what now happens to Dundas (and ChartFX and any other chart control companies for that matter). I guess they have products for other platforms and more specialised charting controls that will keep them in business. If not, they may live to regret the decision to sell their code...
* Actually $1999.99 but it's quite close to $2000 - does the .99 cent/pence ruse actually still work?