Here are some tools to help with literature reviews.
If you are looking to find the most cited articles on a topic or in a particular area; if you have an authoritative but out-dated article and you want to find all the published works that referenced that article you can use ISI Knowledge: Web of Science (If you are logged into UofM library use this link) is a great resource (use 'cited reference search'). UofM library has a comprehensive list of indexes classified by subject category.
ISI also allows you to electronically search through the references in a particular article, and list other related articles by matching articles in reference. It also allows for saving references from a session as a bibliographic text file or importing the references into a online reference manager like RefWorks (UofM now has group subscription for RefWorks).
Google scholar is also good for citation search. Google also lists unpublished articles from online repositories. On the other hand Google is likely to be more up to date.