There is an outstanding discussion taking place at Sphinn now on the topic of providing SEO clients with ranking reports. There are arguments for both side of the debate.
On one hand, to prove your worth the money your clients are paying you - they want to see what you have done for them. You can provide them basic keyword ranking reports to show them that the clients rankings have improved for X number of keywords over time.
On the other hand, you and I know that Google's search results can differ based on who is searching. Google personalizes the results based on a ton of factors including location, previous searches and clicks, web history, social metrics and so much more. So proving a ranking report really doesn't do justice to what the real searcher sees.
Finally, Google provides their own ranking reports within Google Webmaster Tools and soon, coming to Google Analytics. Other means of getting the data is often against Google's terms of service.
That being said, do you provide client's with keyword ranking report. Take our anonymous poll:
Forum discussion at Sphinn.