Here are some websites, tutorial shops on AFF, and a few Deviants, that I’ve found and collected over time. I have found them to be extremely helpful with Gimp and poster making. I hope you do too! :)

Brushes:
- Angelic Trust
- Saruna
- Ego-Box
- Blog Akaleez
- Awesome Style
- A World of Magic
- Caotiicah
- Choking on Static
- Efamous
- Eleven1627
- Expose42
- Kuschelirmel-stock
- LDN755
- MC Bad Shoes
- Meg-Cartshy
- My Shiny Boy
- Skyline Illusions
- The Thiird Shift
- Trapunta
- XVanillaSky
- Zinnia-Aster

Color Palettes: (Color palettes can help you colorize your posters and giving you color ideas for posters. It also helps you match up colors and coordinate them.)
- Colour Lovers
- Bitter Wizard
- Xchanced
- Sultryy
- Sparkle Lust
- Unbreakable
- Insomniaa
- Hex Color Codes (Even though it doesn’t have palettes, it still has plenty of colors for you to choose from.)

Gimp Curves:
- In the Deep Dark
- Wildrune11
- SilaynneStock
- starkbucksfun
- kalitoz

Fonts:
- Dafont
- 1001 Free Fonts
- Abstract Fonts
- Fonts2u
- Moonangel517

Patterns: (Some of these websites have pretty backgrounds that you can use for your posters and as patterns.)
- Cute Backgrounds
- Dollie Love
- Free Glitters
- My Cute Graphics
- Cherry Bam
- Shabby Princess
- Crazykira-Resources
- Ransie3
- Pattern

PNG’s:
- Ulzzang-PNGs (I own this deviantart group and have cut most of them out myself!! ^^)
- Asian-PNGs
- 365
- Shinpanda
- Chaotic Serenade
- PNG Source
- Somewhat Damaged
- Beinspyred
- ChazzieF
- ChantiiGG
- Exclusive Style
- Falling Into Creation
- Francesdotcom
- Gwendo0
- Heeykiid
- Its a Nice Day
- Jaimemin
- Jesuiskieran
- Kinds of Love
- Lets Chill
- Loooree
- Manon Design
- Miss-Famous
- Mr. Raindrop Emmabing
- Noodles809
- Ohsheis Gaga
- One 21 Guns
- Qeezy Baby
- Qianyuanliulan
- Revall Say
- SDouer
- Shineunki
- Salic33
- Siwon Choi
- So Dust
- Snapped Beat
- Spectacular