While at the World Fantasy Convention a few weeks back, the legendary Darrell K. Sweet was the Guest of Honor. He put on an incredible retrospective show, featuring pieces from the 1970's through now, with paintings from some of his highlights: early Tolkien work, Xanth covers, Wheel of Time, and lots of good stuff in-between. I first saw his paintings in the mid-90s at a local convention back in CA when I was still young and impressionable, probably my first year of art school, or around there. I knew his work well already, as it had graced the covers of many of the books I'd read. I'd always assumed he used oils, as his handling and color had a very turn of the century (*that* century, 20c) classical look about it. I was floored to learn he was using acrylics, exclusively. So much the fan was I that I did a landscape study based on one of his paintings (in storage somewhere), in acrylic, to try to learn what his secrets were.
This guy has been illustrating longer than I've been alive, is now in his mid-70s and still working hard. You simply cannot as an illustrator ask for more.
He also had on show, and also for sale, a number of small color studies. Hardly anyone does painted color studies anymore, but Darrell still does. They are in acrylic, too, and are great little gems--detailed while remaining very loose at the same time. A great schooling in acrylic handling. They go for very modest prices, and though while I was a poor student I could not afford to get one (I tried), I am slightly less poor than I was then, so I plunked down a little money and picked up this 8.5x12" painting: