ICONS
http://icons8.com/ - 55,300 free icons. Yes, you've heard it. They're free and although it comes with some size and copyright restrictions.
https://iconpharm.com/ - 9,900 free icons. This one allows you to do multiple edits to icons before downloading them.
http://creativedo.co/FontAwesomePS - Fontawesome plugin right inside your photoshop, vector .svg format.
http://www.flaticon.com/ - A really good web-based archive for icons.
https://material.io/icons/ - A pretty nice collection of material design icons from google.
https://thenounproject.com/ - A really rad collection of icon sets for all kinds of design.
https://mariodelvalle.github.io/CaptainIconWeb/ - A single author created 350+ resizeable icons for your use.


PATTERNS



https://www.toptal.com/designers/subtlepatterns/ - It's an awesome site to get clean patterns from.
http://thepatternlibrary.com - THIS WEBSITE IS AMAZING. Seamless patterns. Just. Amazing.


STOCK PHOTOS


https://unsplash.com/ - Unbelievably HD, beautiful, free photos that you can use.
https://stocksnap.io/ - A nice collection of HD stock photos all under CC0 license.
http://nos.twnsnd.co/ - This one is really cool, it's basically a site dedicated to vintage-type photos, of course, you can use the stocks as well.
https://pixabay.com/ - Don't you just love the CC0 license?
https://www.foodiesfeed.com/ - YOOOO. DESIGN + FOOD. No seriously, this is a lot like food porn. There's a lot of HD food goodies in here.
https://uifaces.co/ - A very useful website where you can basically get photos to use for mock avatars on any 
https://www.photobash.org/ - More royalty free stock photos!


RENDERS
http://www.renders-graphiques.fr/galerie.htm - Mostly anime-related renders.
http://www.stickpng.com/ - A collection of renders for things like games, animes, memes, musicians, etc. 

VECTORS

http://www.freepik.com/ - They have an unbelievable amount of free vectors you can utilize. 
http://vecteezy.com/ - Also another free vector archive, though a little more limited than freepik.
https://undraw.co/illustrations - Amazing crazy find, this website lets you use .svg vector illustrations.
https://worldvectorlogo.com/ - A collection of famous logos for different brands/companies around the world in .svg format!


INSPIRATION

https://webcreme.com - Design inspiration for the mock-up idea hungry designers.
http://littlebigdetails.com/ - For your daily dose of design inspiration.
https://niice.co/ - Just a lot of designs for every category you may be able to think of.
https://www.awwwards.com/ - Best webdesign trends, they're sort of like the grammys for music, except it's webdesign. 
https://logopond.com/ - A collection of really amazing logos to take inspiration from.


COLOR PALETTE
https://webkul.github.io/coolhue/ - Another resource to grab ideas of cool gradient combinations from.
http://www.sankk.in/material-mixer/ - Quite useful for mixing and matching colours for material design, ui/ux. 
http://paletton.com/ - If you were running out of ideas for color combinations, this one really can save you.
https://pigment.shapefactory.co/ - A wonderful looking resource website for picking colors. Palettes are contrast-friendly.
https://coolors.co/ - Another awesome website where you can generate color palettes.
GRADIENTS
https://www.grabient.com/ - Grab a gradient, grabient. Get it? No?... Okay...
https://uigradients.com - A very cool looking website for gradients.


FONTS
https://fonts.google.com/ - Honestly if you didn't know you could get amazing free fonts from this website, I'm sort of judging you a little.
http://www.dafont.com/ - ALL DA FREE FONTS. See what I did there?


RESOURCE PACKS/WEBSITES
https://designbundles.net/free-design-resources - Basically a collection of random resource packs.
https://freebiesbug.com/ - A site pretty much dedicated to giving out free design resources.
http://flypixel.com/ - Has a lot of free design mock-ups and flat designs. 
http://graphicburger.com/ - A lot like freebiesbug and flypixel.
http://dbfreebies.co/ - A lot of the freebies from dribble and behance categorized into one website.
https://medialoot.com/ - Has a lot of nice icon sets and different other resource collections such as .psds, etc.


MISC.

https://vgy.me - I personally use this imageuploader, it's lovely and all around neat.
https://uploadfiles.io/ - I personally use this file uploader to upload heavy files such as .psds for clients.
https://placeit.net/ - It's a pretty cool website to place/edit any type of image into someone's hand using mobile devices. 
https://rapidgrab.net/ - I haven't personally used this website, but it looks like a good alternative for vgy.me.