Controlling Site Template availablity for new site creation

Scenario:
You want to make site template visible depending upon another feature activation.

Solution:
SharePoint provide a lot of different way to set feature dependencies. While deploying the new site definition, you can specify 'VisibilityFeatureDependency' attribute in the WebTemp* file as shown below.

Snippet:

<Configuration ID="1" Title="Client site" Hidden="FALSE" ImageUrl="/_layouts/1033/images/ClientSite.gif" Description="Client site definition" DisplayCategory="ClientTemplates"
VisibilityFeatureDependency="F6924D36-2FA8-4f0b-B16D-06B7250180FA">

<!-- GUID used above is the feature GUID which you want to active before someone can see this site definition -->