Before straying too far into differing methodologies, make sure to take advantage of refactoring to simplify and consolidate your code. Here is Fowler's catalog, the "alpha List of refactorings," each of which can help you improve and manage your C# code.
By learning to effectively design for reuse and by optimizing your application of interfaces, abstract classes, class hierarchies, dependency injection, and similar tools that exist within the standard object-orientated methodology, you may find yourself well on your way to achieving your desired results.
Beyond that, @Chris Smith has already pointed you to the fact that newer versions of C# (3.5 and 4.0) have added several functional programming capabilities that may help you make your code rock!
If you find you like functional programming, give Microsoft's new F# language a try! It's actually more like "object-functional," a mixture of the two methodologies. You may also want to know that you can mix F# and C# in the same .NET Solution.
I also concur with the other commentators that AOP certainly has its uses!