There are still Site Template in SharePoint 2010, but they're no longer .STP files. Instead, they're packaged in .WSP files just like web parts and features. No longer is there a "Site Template Gallery", instead there is a "Solutions Gallery".
To create a Site Template, browse to the Site you want to create from. Go to Site Actions –> Site Settings –> Save site as template (under the Site Actions heading). Give your template a name, and don't forget to check the "Include Content" box if you want to include library and list content in the template. This will create a new site template in your Solutions Gallery, which you can then use when creating new sites. You can also download directly from the Solutions Gallery to a .WSP file.
To upload a Site Template to the Solutions Gallery, go to Site Actions –> Site Settings –> Solutions Gallery (under the Galleries heading). On the Solutions tab of the ribbon, click "Upload Solution". Before you close that dialog, you'll need to click "Activate" to activate it if you want your Site Template to appear in the "New Site" dialog later.
To use the Site Template, go to Site Actions –> New Site. You'll find your Site Template in the list of Installed Items, in the All Categories or Blank & Custom filters.