AOP is a great way to clean code, well if used correctly. lots of examples will only show the logging example, when an exception is thrown (I should know here is one I wrote: hello world of AOP). Well thats ok, you can see it in action and step through it, however that for me was not enough. So here are a few more really helpful links

• AOP Guide - Spring.Net, this is great intro guide.
• 7 Approaches For AOP in .Net - this goes over the different ways AOP has been implemented for .Net
• Simple Aop Example user DynamicProxy 2.0 - Castle DynamicProxy, David has written the basic logging example, but I liked it and thought it was easy to read.
• An Impersonation Aspect With Spring.NET AOP - Spring.Net, goes through a great example of security with AOP
• Dirty Tracking - Castle DynamicProxy, using AOP to track when an object should be marked for dirty
• AOP MSDN - Quick Guide on the different types of Aspects
• AOP Programming Examples - question on StackOverflow
• Design Patterns with AOP - for Java but worth the read