Фотостоки:

https://freestocktextures.com/texture/
https://ru.freepik.com/
https://unsplash.com/
https://www.pexels.com/
https://www.goodfreephotos.com/
https://pixabay.com/
sxc.hu
Dreamstime.com/free-photos
freerangestock.com
morguefile.com
stockvault.net
everystockphoto.com
creativecommons.org
fotolia.com
istockphoto.com
photogen.com
firestock.ru
vintagepixels.com

Иконки:

http://ionicons.com/
https://linearicons.com/free
https://ru.freepik.com/
https://iconmonstr.com/
https://iconstore.co/
https://thenounproject.com/
http://fontawesome.io/
https://www.iconfinder.com/
https://www.flaticon.com/
https://glyphicons.com/
https://octicons.github.com/
http://s-ings.com/typicons/
http://fontello.com/
https://icons8.com/
https://icomoon.io/

Шрифты:

https://fonts.google.com/?subset=cyrillic
http://fontpair.co/ - шрифтовые пары
https://fontstorage.com/ru/category/
http://www.myfonts.com/search/cyrillic/free/

Цвет:

http://www.vanschneider.com/colors
http://www.colourlovers.com/palettes
http://www.colourlovers.com/web
http://www.0to255.com/
http://colorhunt.co/
https://coolors.co/browser/latest/1
https://www.materialpalette.com/
http://colovely.nofach.com/
https://www.webdesignrankings.com/resources/lolcolors/
http://www.colourlovers.com/web/trends/websites
http://www.colourlovers.com/web/colors
http://www.colourlovers.com/web/palettes
http://www.vanschneider.com/colors
https://coolors.co/
https://coolors.co/browser/latest/1
https://dribbble.com/
http://paletton.com/
https://color.adobe.com/ru/create/color-wheel/
https://colorscheme.ru/
https://color.adobe.com/ru/explore/?filter=most-popular&time=month
https://dribbble.com/colors/109121
http://www.pictaculous.com/
http://www.degraeve.com/color-palette/
http://palettegenerator.com/
https://bighugelabs.com/colors.php
http://tulkindom.ru/tablica-sochetaniya-cvetov
http://heaclub.ru/sochetanie-cvetov-v-odezhde-tablica-sochetaniya-cvetov-odezhdy-dlya-zhenshhi

Фон:

https://freestocktextures.com/texture/
https://www.toptal.com/designers/subtlepatterns/
https://www.toptal.com/designers/subtlepatterns/thumbnail-view/
https://www.textures.com/
https://www.patterncooler.com
http://thepatternlibrary.com