For some reason or another I’ve been able to creat a new site then save it as a template in both SP2010 and SP Designer 2010…except all of a sudden.  Not sure why, but when I exported an existing site from another farm (identical SP2010 installation), then imported it into another SP2010 farm the option is gone.  This also happened when I tried uninstalling the template from the Solution Gallery then redeploying it into the same farm.  Fortunately, I happened to find a solution that worked for me here.

Basically, navigate to the website in question (the one you want to save as a template) and append the following url (in bold):

http://server/site/_layouts/savetmpl.aspx

Here’s the caveat-DO NOT do this for Publishing sites!  It’ll work with a Publishing site, but when you try to create a new site out of it, it’ll break.  This is because the site template expects a normal URL structure, but the Publishing site puts pages inside of a pages library.

To deactivate, modify or delete other site templates, go to http://server/_catalogs/solutions/Forms/AllItems.aspx

Hope this helps!