This simple script will list all of your entries in your crontab file, and allow you to choose which one to run immediately.

cron-now.py

#!/usr/bin/env python

from subprocess import call, Popen, PIPE
import re


def main():
    """
    Prompts the user which cronjob they would like to run, then
    runs it in the shell.
    """

    # Retrieve the list of cron jobs from the shell
    p_crontab = Popen(["crontab", "-l"], stdout=PIPE)
    cronjobs = p_crontab.communicate()[0].split("\n")

    # Filter blank lines and comments
    re_comment = re.compile(r"^#")
    cronjobs = filter(lambda x: x != "" and not re_comment.match(x), cronjobs)

    print "Which cronjob would you like to run?\n"

    # Build a numbered menu of cron job commands
    i = 0
    for job in cronjobs:
        i = i + 1
        command = parse_command(job)
        print "  %d) %s" % (i, command)

    print "  q) Quit. Do not run anything.\n"

    # Process the users input
    while True:
        run = raw_input("Enter number: ")

        # The 'q' option will quit
        if run == "q":
            break

        # If a valid option is specified, run the command and quit
        if run.isdigit() and int(run) > 0 and int(run) <= len(cronjobs):
            command = parse_command(cronjobs[int(run) - 1])
            print "\nExecuting: %s" % command
            print "=" * 80
            call(command, shell=True)
            break
        # Otherwise repeat the loop
        else:
            print "Error: Invalid option"


def parse_command(job):
    """
    Given a single line in crontab syntax, return the command.
    """
    parts = re.compile(r" +").split(job.strip())

    command = ' '.join(parts[5:])

    return command


if __name__ == '__main__':
    main()