You've heard plenty about the Sterling database engine on this blog. I recently released version 1.5 which extended the reach of the database and added several feature requests. My article on Sterling for Isolated Storage on Windows Phone 7 was also recently published in MSDN Magazine. The phone has made this a very popular engine and it has been used in several production applications that you can read about in this discussion thread.
Telerik is a vendor that provides controls and tools for developers. I've used them in projects myself and favor them for Silverlight development because they are developer, designer, and MVVM friendly. In addition to controls, they provide an ORM, code analysis tools, unit mocking and testing aids, and even a free .NET decompiler. I'm also impressed by how involved with the development community they are, sponsoring many events including the one I recently spoke at, CodeStock.
My favorite feature ... "Using SterlingDB for a blazing-fast app"
The application uses a Telerik control with a virtualized stack panel bound to a Sterling query. Because Sterling uses lazy-loaded queries (the indexes are loaded in memory but the details aren't loaded from disk until needed), the list box can scroll literally thousands of tasks ... fast. This is because the virtualized controls are bound to the lazy details, so deserialization only happens when the specific task comes into the view. You have to pull it down and play with it to see for yourself.
That's one continuous set of text (feel free to provide separate hash tags for #telerik and #wp7 as well, but the tag #telerikwp7dev is what will make you eligible). Telerik pick 10 tweets that include the tag, contact the person who tweeted it and provide the details for the license.
I can't think of an easier way to pick up a set of awesome controls than to share a sample project with full source code that demonstrates an integrated Windows Phone 7 application that operates across a large, local data set. Good luck!