(I apologize for the posting delay, my days got a little busy and ran away from me).
So to continue from Wednesday on the stylings of illustration, here a few more to consider:
Oil / Renaissance / Traditional / Painterly - Traditional really is in the eyes of the beholder but it can also signify what one may think of as renaissance style and "traditional" oil paintings (reminiscent of master artists - Delacroix, Monet, Vermeer, Velázquez, etc.). The enticing element to this style is the texture that comes across in the artwork as well as the richness of colors.
Glenn Harrington and Shawn Barber are good modern day examples of this style.
Digital / Computer / Graphic - This is illustration that is done with computer programs (hence "computer" style). It's stylized and usually has a more modern feel or a cartoon-ish feel. The edges are sharp and the colors are tight and bright. Check out Kirsten Ulve and Michael Clampton.
Retro - This style references more of what we think of as pop art, art deco, and recent historical art style from the 1920's through the 80's. It's a similar style and techniques from the recent past.
See the work of illustrator Dave McMacken or the rep agency Retro Reps.
There are so many styles and so many mediums and even more great illustrators.
Explore books like Showcase, Workbook, Communications Arts or blogs like Drawn!, IllustrationMundo, and Illustration Friday