The solo: Big Agnes SeedHouse SL1
This tent has been my go-to solo tent since 2003 for 2 simple reasons: weight and functionality. This little badboy is freestanding, super-lightweight, bugproof, long enough for tall folks, stormproof, has a vestibule, as a fastpack option (footprint and rainfly only when bugs are not of concern), you can sit up in it, and its an awesome stealth green for low-impact camping. At just a hair over 2lbs for the whole tent and considerably less for the fastpack option this is just about the lightest freestanding solo tent out there. The bathtub floor keeps out splash from driving rain and ample guyout points allow for a super-taught pitch when conditions (rain and/or precip) warrant. It should also be noted that this tent comes in 2 and 3 person versions as well that perform just as admirably.
The Double: Six Moon Designs Europa II
With enough space for two adults, all their gear and a dog inside you'd expect for a shelter to come in weighing more than 4 lbs - howzabout less than 2 lbs? Now don't get too pumped because the Europa II is no longer produced. The one I have is from 2004 and has been discontinued (although I can't imagine why), but there are others out there that are similar. Golite, Six Moon Designs, and Tarptent are all manufacturers that produce a similar shelter using trekking pole support(s) to save on weight and guylines to provide tension and structure. While a step up from a tarp in that these shelters offer bug protection, these shelters are minimalist. In fact, the Europa doesn't even have a front door! However, despite the light weight and simple lines, these things stand up very well to the elements and when pitched correctly can (from experience) withstand tropical storm rain, hail, up to 2" of snow, and 20+ mph winds. With ample venting, these shelters also have negligible condensation problems, even with a single wall of non-breathable sil-nylon. The closes thing to the Europa II that I've found currently in production is the Tarptent Squall 2. Its a little more robust (it even has a door!), but still weighs in at a mere 34 oz.
The Triple (sort of): Black Diamond Skylight
Alright so the 3 person status of this tent has to be qualified because I've not yet tried to cram 3 people into it with the exception of myself and my 3 and 5 year old little girls. I think its safe to say that it'd be a friendly fit for three, but with a decent vestibule, great head space and ample length it could certainly be done. Now enough qualifying: Black Diamond makes an awesome line of single-wall tents called their Superlight series. By eliminating the traditional double-wall (body and rainfly) design using waterproof breathable Epic by Nextec fabric, Black Diamond has been able to offer more tent for less weight. With the Skylight you get a 2-3 person, freestanding shelter that guys out tight enough for 3+ season use. The vestibule is a good size and the best feature is that the front 2/3 peel back for mesh-only ventilation and views in good weather. At just a hair over 4 lbs. this is my heaviest tent by far, but 4lbs. is still ridiculously light compared to most industry standard 2 person tents, let alone 3 person tents. With the supplemental seam-sealing recommended in my previous post this tent is a high-performance bomber of a tent.