Sitecore has a button on the developer tab that allows you to re-index just a portion of the content tree. This can be handy to avoid a full index rebuild when you have a large content tree or if you are debugging custom indexing funtionality likc computed fields. Unfortunately, the button causes the the subtree to be re-indexed for all indexes. A few MVPs were recently tweeting about how it would be nice to have the option to select a particular index. I just happened to have written a Sitecore PowerShell Extenstions context menu script to do this recently.
This script lets you select one index to refresh for the selected subtree. Note that it just starts the job and closes the window. It does not monitor the job’s progress. You could add this if you desire or simply use the jobs admin page. The script needs to be saved under /sitecore/system/Modules/PowerShell/Script Library/Content Editor/Context Menu after you have enabled the context menu integration point in the module.