Key questions to ask:
• How big is the water spot?
Water spot is toiletspeak for how much area the water covers in the bowl when it's full. Some low-water toilets, like the Caroma brand, save water by reducing the amount in the toilet bowl, which is great for the earth, but can result in another toilet euphemism called "bowl streaking." (This is easily remedied by keeping a brush handy, but that's a behavior change you must honestly assess if you are ready to make.)
• How much water does it use?
Some dual flush toilets use 1.6 gallons of water on a big flush, and .8 gallons on a small flush. Others use 1.6 gallons on a big flush, and 1 gallon on a small flush. The difference adds up!
• What if it breaks?
Toilets are fairly simple mechanisms, but if yours stops working, you want to make sure it can get fixed right away. Ask where replacement parts are stocked.
• Does it plug in?
Kohler's Power Lite technology uses an electric pump to boost flush power, so the toilet requires a power outlet... which seems strange to us. Also, sometimes, toilets that plug in are LOUD.
Images and links to a few dual-flush toilets after the jump—please add any we've missed.
• Caroma's line of toilets is more complete, but availability of the full line can be spotty. More expensive, too, but we love the innovative mounting system on some of Caroma's toilets that eliminates nasty cleaning around bolts and surprise leaks. From $350 and up at BuyPlumbing. 1.6 gallon big flush/0.8 gallon small flush.
• Kohler's Power Lite toilets offer a dual flush option. The Hatbox, shown above, has no tank and drops straight to the floor: minimal and easy to clean. Lists at over $3000, but most plumbing stores and big box retailers offer a discount. For a less expensive option, check out the San Rafael, a more conventional one-piece design starting at less than $1000. 1.6 gallon big flush/1.0 gallon small flush.
A note on shopping online: shipping heavy things, like toilets, can cost serious money. When comparison shopping, make sure to add in the price of delivery, and consider buying from a local store even when the price is a little more; you will want your local plumbing shop to be in business if you ever need a replacement part right away!