I don't think there is any specific site for genuinely this purpose. Ofcourse google sometimes give you an option to choose if the keyword is mis spelt.
No site can tell you how often a keyword is searched, Google don't want to reveal it, their keywords tool gives an estimated volume of search and so do some other services like Word Tracker. I personnaly use and recommand my own tool that you can find on SEOKeywords.110mb.com .
There's not much figures to read for misspell keywords. BUT, you would be able guesstimate when comparing the misspell search terms with the popular related keywords at Google Insights. A rough overview but I found it pretty useful.
I was going to concentrate on misspelling but have been advised against this by many people, think i will steer clear now.
If you use a keyword search tool then it can tell you what you are looking for. I have been a tool which can be found out here http://www.serpanalytics.com/tools/top_keywords and it can tell you everything even CPC, number of searches and many more for any of the keyword you enter...
Google keyword selector tool... will be da best keyword research tool to find out the best keywords for your website keyword selection process.