Search Documents Citing Case or Article in Google Scholar
Google Scholar has a feature that allows you to view documents that cite to your case or article. This is somewhat akin to Shepards, although without the status indicators and comprehensiveness.
Recently, Google has beefed up the "cited by" feature by allowing you not only view the citing cases and articles, but also do a full text search of them. It can also be used to limit the results to citations from specific jurisdictions (via the dropdown on search pages or the advanced search page).
In your initial search results, click on the "Cited by ---" link below the item.
This will open a new search window at the top in which you can do a full text search of the documents citing that case or article.
Source and images: 3 Geeks and a Law Blog