One of my favorite palettes is the earth palette. It's one of the most limited palettes you can find, and it really forces you to be subtle with your colors. When painting with it I find I have to really grey down everything as much as possible, saving those vibrant accents for the end.
"Papago Rocks on Pallet Wood" Oil on panel, 6.5x12
The palette I'm using here is (from left to right), Ivory black, green mixed from ivory black and yellow ochre, yellow ochre, orange mixed from yellow ochre and terra rosa, terra rosa, burnt umber, mars violet, purple mixed from mars violet and ivory black.
The advantage of this palette is the cost. Earth tones are almost always series 1's. Everything also tends to be very opaque and fast-drying, making these colors ideal for underpaintings.
Here is an old cast study, painted using the same palette. I think this one had Venetian red in it as well.