You can do excellent macro work with your lens, especially with a few relatively inexpensive additions. Get a +3 or +5 diopter filter and a set of extension tubes. That will get you some nice close images but will likely require a tripod to make them tack sharp.
One rule of thumb for flowers is find really perfect subjects or really dead ones, the in between ones don't make the best "artistic" images.
On your first image try a little more crop to get rid of the two right sided corner "triangles"; see if you like that better.
I like the flower position in the second to last image, but the background is a bit to busy.
Nice work. (Here is a 70-200mm lens with a +3 diopter and extension tube. No flash.)
Last edited by SMB; 11-14-2012 at 05:09 AM.