Here are some common aspect ratios and resolutions that I'm always on the look for.

2k

Frame Aspect Ratio  /  Resolution (Square Pixels 1.0)

• 1.33:1 (4:3)  /  2048x1536
• 1.66:1 (5:3)  /  2048x1229
• 1.77:1 (16:9)  /  2048x1152
• 1.85:1  /  2048x1107
• 2:1  /  2048x1024
• 2.35:1  /  2048x871
• 2.37:1 (RED Wide)  /  2048x864
• 2.39:1 (referred to as 2.40)  /  2048x858
• 2.44  /  2048x839

1080p

Frame Aspect Ratio  /  Resolution (Square Pixels 1.0)

• 1.66:1 (5:3)  /  1920x1152
• 1.77:1 (16:9)  /  1920x1080
• 1.85:1  /  1920x1038
• 2:1  /  1920x960
• 2.35:1  /  1920x817
• 2.37:1 (RED Wide)  /  1920x810
• 2.39:1 (referred to as 2.40)  /  1920x803
• 2.40:1 (Blu-Ray)  /  1920x800
• 2.44  /  1920x787
• 1.33:1 (4:3)  /  1920x1440