Tamir Lousky shares a script for creating HDR-like image lighting in Blender, that can dramatically speed up your renders by faking HDR lighting based on an input image.

a script that fakes the lighting produced by (commonly HDR) environment images

The script essentially takes the colors from an image (or IBL) and creates a light array with lamps that will emit colors that are taken from that image. Tamir notes that this can reduce the render time for Blender Internal by more than half and get a fairly similar result to an HDR image. Check out the FakeHDR Script for Blender here.