at Bed bath and Beyond, I saw a toothbrush holder that was quite modern in style--a smooth block--that had 3 big square holes. I'm not sure if they were *quite* big enough for electric toothbrushes, but they were clearly intended to hold fat-bottomed toothbrushes.
(the white is out of stock, but the orange is still there)

But there's this one, that's more elegant (painted to look like oil-rubbed bronze)
it holds 2

If I were a potter or a woodworker who had any inkling to do craft shows, I'd be making toothbrush holders for electric toothbrushes!

We just sort of prop ours up against the back wall of the medicine cabinet.

I also want to make a horizontal toothbrush rack that will fasten to the back of the medicine cabinet door, so you can lay several of them flat between the shelves.

We have drawers in our vanity. Since I hate having the brush heads out in the bathroom air we keep ours in a rubbermaid silverware tray in the top drawer. You know the kind with 5 oblong spaces.
This works perfect. Everyone can keep their toothpaste along with the brush heads in their spot and was only 2 dollars at Big Lots. :)

My electric toothbrush came with a plastic holder with for two brushes to sit in a wide round space. I keep it in a cabinet as I don't like toothbrushes out.

You can also buy a traditional fancy toothbrush holder and put the brushes in, brush side down, instead of up. The brush heads on electric are smaller so they will fit that way. Don't use the ones with an enclosed base or there will be no air circulation. Get one open maybe like this:
http://www.amazon.com/Brushed-Metal-Toothbrush-Holder/dp/B0006V57HO/ref=sr_1_3/104-4173497-6226323?ie=UTF8&s=bedbath&qid=1176842535&sr=1-3

Or get one where the brushes push in at the neck like this:
http://www.amazon.com/0733-10b-circa-tumbler-with-toothbrush/dp/B000NMB5V8/ref=sr_1_133/104-4173497-6226323?ie=UTF8&s=bedbath&qid=1176842849&sr=1-133

You can get countertop ones where the brush pushes in at the neck. I used to have one but can't find it online for a pic.

Here is a link that might be useful: Push in toothbrush holder.

Here's what I did with mine -- I had a 6" square tissue box cover I wasn't using. One day I spotted it stored away in my linen closet and thought it would be the perfect cover for the toothbrush. I popped it over my toothbrush and it was almost perfect -- it's way bigger than necessary, but very pretty with my other sink accessories. A big plus -- you have hundreds to choose from.

We have the cutest toothbrush holder (ceramic), but now that we use electric toothbrushes, we can't use it. Grrrr! So I bought two little plastic baskets at the supermarket, the kind that are sold in the same section as the hairclips. They are translucent green, maybe eight inches long and three inches wide. This makes them perfect for putting in the medicine cabinet to hold a toothbrush and toothpaste. Problem solved!

there is a toothbrush holder for Electric toothbrushes called the cloverholder, and its made in America, won't break if its
knocked of the counter. Holds 98% of all electric toothbrushes
on the market. Only sold on the internet. www.cloverholder.com

I just save the protector that comes over the top and after rinsing and shaking it dry i lay it next to my tube of paste on the bottom shelf of my med cabinet..works for me.After hearing that when you flush the toilet even if you close the top that a mist floats through your house on the air currents..well i decided the more doors between the toilet any my toothbrush the better

LOL -- this thread has been "revived" after two years. In that time, we gutted and remodeled two bathrooms, and thanks to the suggestions above, I included plenty of storage space to dedicate a drawer to toothbrushes, toothpaste, floss, and the like. Toothbrushes and toothpaste rest in a mesh flatware tray -- with a washcloth underneath to catch drips. I LOVE not having these items on the counter top.