Vallejo Scurvy Green - an amazing color that can be used to add depth to just about anything.

AK Light Flesh - a great off white to mix into other paints for highlighting

Vallejo Metal color Silver - the best metallic paint than can be covered with inks or contrast to creat any metal color.

Contrast Blood Angels Red - a way to bring the red richness back with glazing

Vallejo Game Color Lustful purple -- a interesting base shade for whites. Highlight up with Light Flesh for an interesting white.

Vallejo Model Color Black: It's a bit boring to say, but it's definitely my most used color.

Vallejo Game Color Scrofulous Brown: Great for my Yu Jing, but also pus, fire OSL, Gold NMM, and various other applications. It's so nice in a glaze.

Citadel Doombull Brown: It's just a very satisfying color for me. I use it all the time, especially for leathers and the occasional rust.

AK's Ice Yellow. When in doubt, I just mix this in for a highlight color.

Dark Reaper / Dark Sea Blue. I just need a dark blue-gray all the time either as a shadow color or as the first highlight for black.

Honorable mention: Blood for the Blood God.

Citadel Mephiston Red

Pro Acryl Bold Pyrrole Red

Pro Acryl Bold Titanium White

Two Thin Coats Sir Coates Silver

Scale75 irati green

I really like Vallejo burnt red.

Vallejo black (super basic I know)

Vallejo German cammo dark green

Vallejo Metal Color gunmetal grey

Citidel Retributor armor.

These are just the ones I use a lot and enjoy using. I also really like ProAcryl for vivid base coats. Citidel paints are great for dry brushing. Don't use contrast very often but recently discovered that I get really nice yellows by painting something skin tones and shading before finishing with one of citidel's yellow contrast paints.