Too many to enumerate - but I'll try and summarise.  Briefly, there
are several decisions you have to make, including:
  * Power.  Is it up to a complex task?
  * Complexity.  How much programming manpower is it worth?
  * Portability.  Might you want to run your program on another system?

So here's an overview of the main options.  It's inevitably subjective,
but may be helpful to someone:

Basic SSI:		Simple interface for basic dynamic content.
			Non-standard - read your server docs.
Enhanced SSI[1]:	Suitable for more complex tasks within
			an HTML page.
CGI:			The standardised, portable general-purpose API,
			not limited to working with HTML pages.
Enhanced CGI-like[2]:	Typically gain efficiency but lose portability
			compared to standard CGI.
Servlets:		An alternative API for JAVA, that overcomes
			the limitation of JAVA not supporting
			environment variables.
Server API:		Generally the most powerful and most complex option.

[1] For example, PHP, ASP.
[2] For example, CGI adapted to mod_perl or fastcgi.