Just type "django-profiling" on google, you'll get these links (and more):
http://code.djangoproject.com/wiki/ProfilingDjango
http://code.google.com/p/django-profiling/
http://www.rkblog.rk.edu.pl/w/p/django-profiling-hotshot-and-kcachegrind/
Personally I'm using the middleware approach - i.e. each user can toggle a "profiling" flag stored in a session, and if my profiling middleware notices that a flag has been set, it uses Python's hotshot module like this:
def process_view(self, request, view_func, view_args, view_kwargs):
# setup things here, along with: settings.DEBUG=True
# to get a SQL dump in connection.queries
profiler = hotshot.Profile(fname)
response = profiler.runcall(view_func, request, *view_args, **view_kwargs)
profiler.close()
# process results
return response
EDIT: For profiling SQL queries http://github.com/robhudson/django-debug-toolbar mentioned by Konstantin is a nice thing - but if your queries are really slow (probably because there are hundreds or thousands of them), then you'll be waiting insane amount of time until it gets loaded into a browser - and then it'll be hard to browse due to slowness. Also, django-debug-toolbar is by design unable to give useful insight into the internals of AJAX requests.
EDIT2: django-extensions has a great profiling command built in: