Running Django with FastCGI or with mod_python
lighttpd with FastCGI will be nominally faster, but really the time it takes to run your python code and any database hits it does is going to absolutely dwarf any performance benefit you get between web servers.
mod_python and apache will give you a bit more flexibility feature-wise if you want to write code outside of django that does stuff like digest auth, or any fancy HTTP header getting/setting.  Perhaps you want to use other builtin features of apache such as mod_rewrite.
If memory is a concern, staying away form apache/mod_python will help a lot.  Apache tends to use a lot of RAM, and the mod_python code that glues into all of the apache functionality occupies a lot of memory-space as well. Not to mention the multiprocess nature of apache tends to eat up more RAM, as each process grows to the size of it's most intensive request.
which would you recommend?
which is faster, reliable?
apache mod_python or nginx/lighttpd FastCGI?