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My oldest paints are the Winsor & Newton Cotman paints, a student line but they seem to be of fairly good quality and have some nice colors. I've done at least a dozen ink and wash paintings using only the W&N paints you see here: earth colors. They work well together and are great for sketching/painting landscapes and fall scenery.
The Van Gogh and Grumbacher paints are also student paints that I pick up sometimes at art stores when they're on sale. You can find them extremely cheap and they seem to be very good paints for the money. For around $2, I can't find anything to beat them for cost/quantity/quality in a student paint for sketching or adding color to ink drawings.
I really like the Maimeri Blu paints. Their Cobalt Blue is completely awesome even though it's really expensive, and their Cadmium colors are very vibrant, the only fault I have with them (Cadmium in general as a watercolor pigment) is that they are so opaque. That does have its uses, though.
The blue is a bit grainy but really potent, it mixes up some nice purples or greens with ease.
The earth colors are good. I strongly recommend you at least try their blues and siennas. From what I've red, they make some good violet colors as well.
Viridian is a nice sea-green color and I've found it useful for painting plants.