There's the 'pmccabe' tool, which can check for # of lines of functions and their cyclomatic complexity.

Then,

  pmccabe `find . -name '*.c'` | sort -nr | awk '($1 > 10)'

gives me all functions that have a cyclomatic complexity over 10; I often add it as a target in a Makefile, so I can easily check this. Similar, for functions of a certain length.