Just found out about pyflakes at work, and installed the pyflakes-vim vim plugin. Wow. I had no idea how sloppy I was coding!
I have been learning go lately, and one thing I love about their compiler is that they don’t let you write sloppy. Import something you forgot to use? It’ll tell you about it. Declared a variable you decided not to use? It won’t let you make an executable until you fix it. Pretty cool stuff.