I've got an application with about 35~ different settings in different categories.
What are the best practices to expose this to the client.
Secondly is there any VS.NET add-on or library (commercial or not) which can help to speed up this process. Something like "Property Grid" maybe but with a more professional and user friendly look.
All of the settings based on a class and couple of subclasses.
Have you looked at the design implemented by Visual Studio itself which is a tree view for the categories and a panel that updates when each category is selected?
I haven't been able to find any examples on Code Project (I'm probably searching for the wrong terms), but I have found this tutorial which walks you through three different visualisations. It's dated 2004 so there are probably newer pages out there, but it'll be a good starting point.
For only 35 options, I would think a standard tabbed options dialog would work fine. It is a familiar interface that even novice users understand.
However, for applications with many options, this type of interface starts to break down. You end up with too many tabs or too much clutter on each tab. The options screen in Word 2007 is slightly better for a large number of options. It is essentially a tabbed interface, but the tabs are on the left instead of the top and the area on the right is scrollable. You want to be careful to put the most important options "above the fold" so they don't get lost. Also, having a "Popular" tab is a good idea.
If you expect your number of options to grow, you may want to consider an Office 2007 style options screen.