When I started this list back in 2006, small toilets were hard to find and water conservation was not a big concern. Times have changed. I've updated our list from great comments collected over the past year. Check out new additions from Caroma, and a really good critique of Duravit that we've also witnessed. Got good info on toilets? Add it to the comments and join the conversation.
The big issue that I've seen with low-flo and stylish wall-mount toilets is that they can not clean themselves out very well - requiring additional flushes. Redneckmodern has seen this specifically with his own Duravit's:
i'm a big fan of the look of the duravit toilets (we have 2)... we have a stark-3 which is very similar to the happy-d... one thing to note: i find it doesn't flush well... not nearly as well as the toto toilets (by a large margin... and we've had 2 (in our old place). upon inspection of the duravit and comparison, it seems the "neck" (where the toilet outlet meets the floor flange) is actually smaller than most others and there's actually a lip where "stuff" gets "snagged"... odd that is isn't a smooth transition. net result: while it looks wonderful, it fails more often than not at what a toilet is s'posed to do. - Redneckmodern
• MiniLOO by Neo Metro
The MiniLOO uses an in-wall tank system, saving lots of space in the bathroom. The look is super simple and streamlined, and is available in a choice of finishes...
• The Starck 2 Toilet
My favorite looking toilet, Starck 2 has been installed by posters to this site: All in one version and in Two piece "space saving" (you need larger than normal air space in your wall or you need to build your wall out thereby losing space) wall mounted version - Jamie Pup
• Duravit Happy D
...projects 21.25" from the wall but I think it runs around $1000 and requires a plumber to install the tank inside the wall. - Yen Ha
NOTE - Toto seems to have revamped their whole product line for toilets and we could only find the Aquia from our list on the Toto site. However, the other models, Dorian and Ultimate, were found from other sellers, so they must still exist.
• Toto Aquia
Gotta add the Toto Aquia to the list. It's relatively new, but it's available. Small tank, very nice design, and also a water-saving dual-flush model (so it has a smaller, 0.9 gal flush as well as a regular). Pilgrim
• Toto Dorian
It's great, nice and small and uses very little water. It has "power flush" and is really quiet. Sasha
• Toto Ultimate
The best small medium priced toilet I've heard of is the Toto ultimate (about 250$ 2 1/2 years ago). I polled residents in my building when I needed to change to a low flow model upon purchasing a unit I'd been renting and this model won. - Jonathan D.
• Kohler Rialto
...quite pleased. It is compact and flushed well. I would purchase it again if I were re-doing another bathroom. - Lonnstrom
• Purist Hatbox Toilet from Kohler
...You know, it sort of looks like sitting on a small trash can. But it is small.- AT
• Veneto Toilet: This slim toilet is made by Porcher and was sent to us by Laura Dixon, who calls it "lovely and small."
• Caroma Adelaide and Brisbane: "I would like to add [these] to your line of small toilets. Caroma is a world leader in dual flush technology and does not produce a single toilet line without this important technology." - Andrea P.