I've been watching people post HDR images for months, and I recently stumbled upon Meet the Gimp: Episode 25 which discusses exposure blending. The hard part was defining a clean mask for blending the images.

It's not the crazy tone-mapping stuff, but this technique allows for some relatively natural looking changes.

Blending can be done by copying the layer with the most contrast (or darkness), and applying a Threshold to it, and adjusting the slider to get a clean edge. Then invert, and copy that black-and-white threshold image to be a mask for your top layer. A little hand painting and Gaussian blur finishes up the mask, and it should look pretty decent.

My sunflower image is an example of using this technique with 3 exposures pulled from one RAW image. The threshold and blur helped immensely to help define the edge between plants and sky with minimal halos.

Wall-E is another example, but I used the technique to blend different saturations for emphasis of the subject, and deemphasis of the background.

I've recently noticed a few Exposure and Blending Mask options in Gimp's Photo filters, but I've not had a chance to see what they do -- maybe it's the more automatic way to do some of this stuff.