The returned strings can be found in the source code (of course!), this is the list I found (using [ http://lxr.php.net/ident?i=sapi_module_struct ]):
- aolserver
- activescript
- apache
- cgi-fcgi
- cgi
- isapi
- nsapi
- phttpd
- roxen
- java_servlet
- thttpd
- pi3web
- apache2filter
- caudium
- apache2handler
- tux
- webjames
- cli
- embed
- milter