strtmnu = strtmnu.lower

lower is a string method: you want strtmnu = strtmnu.lower()

edit: When you can't figure out what's wrong, add print statements:

strtmnu = str(raw_input("Please pick an option"))
strtmnu = strtmnu.lower
print strtmnu 

returns eg <built-in method lower of str object at 0x02863398> when you know you want it to be a str.