Sitecore ContentSearch exclude standard values
Using the SearchContext class within Sitecore the result collection brings back the standard values item along with any items that are matched.
To solve this problem you can add a computed field to the Lucene index to return a bool property to Linq to say whether the item is a standard value of not.
This means you can search and exclude standard values like this.
Add the following tag to the AddComputedIndexField section of your index.
Here is the class that adds the computed field to the index