If you're a knitter with plenty of va-va-voom and you like to look very feminine,
White Lies Designs is great. Designer Joan McGowan-Michael describes herself as 'deliciously ample', and she certainly knows how to design knits for larger ladies as well as smaller ones, with some patterns on her site starting at 30 or 32-inch busts and many going up to 58-inch busts or more. I love the Madeline Wrap and Heirloom Lace Jacket, although I'm not sure I'm a skilled enough knitter yet to manage either!
Everybody's figure is slightly different, even among people who share a dress size, with some having more volume around the waist, others on the bust and hips. Many commercial patterns are a bit, well, boxy, which is great for athletic builds but not so hot for hourglasses or people with their weight at the top or bottom. On her blog, Joan put a link to this
nifty little tool at Interweave Press' website which will help you nip in the waist or alter the hip or bust size on a pattern. You'll need a tape measure in order to check your own measurements, and note that you will not get an amended pattern, you'll have to work the increases and decreases into the commercial pattern yourself. (I'd probably write out the pattern row-by-row to be sure that I got the increases and decreases in the right rows, although more experienced knitters may well find it easy to keep track of all the changes in their heads.)