Graphic Burger 'Tasty design resources made with care for each pixel', they say. If you need a bag, a coffee cup, a beer label, they will have your mockup image, for free. Just download the .psd, the UI kit, the icons, the 3D photoshop text effects, the background image, the wordpress template. You name it, they have it.
Speaking of templates, with Bootstrap you will save yourself hours of work creating a mobile first responsive design for the web. Thank me later.
Icons? We need icons. The Noun Project will have all the icons you can think of and then some.
Invisionapp is a design prototyping tool where your clients can comment directly on your work. When collaborating on things, this is extremely useful.
Also, nag everyone you know to get your portfolio on to Working not working. It's like a VIP Linkedin for creatives only.
The amusing illustration showing the difference between Art Directors and Copywriters comes from Digital Synopsis. Know of more useful tools out there? Comment.