Selling at art & craft shows, I "float" all of my wall hangings. The simplest way I've found is to mount the print onto a warp-free board, then use a spacer behind the board. I've used Gatorfoam & Styrene, from Coda. Here's a link -http://www.codamount.com/
Look under Mountboards.
The print needs to be laminated, since no glass is used. For the spacer in back, I use a (cheap) 3/4" square wood frame from my local framer. I buy the frames a few inches smaller than the mounting board, and use a strong adhesive to glue it to the back of the mounting board (note - back of frame to back of mounting board). The rabbet cut on the front of the frame acts as a perfect hanger. On a 24x36 board, I use a 16x24 frame in back.
On the wall, the spacer frame "floats" the board 3/4" away from the wall.
You can go an additional step by placing your mounting board and spacer within a larger outside frame. This gives the impression that the print is floating inside the frame.
It has also become popular to have museum grade acrylic adhered to the front of the image rather than a standard laminate.
Bottom line whatever creative way you choose - apply a protective coating to the front, use a warp-free board, and a spacer behind.