I too have used the Tioga Factory DH 2.1's and loved them, but concur they are heavy. I weighed mine, not on the best scale, but ya, they're close to 900g (the 2.3's are definitely 900g, but the 2.1's seemed about 850g - both of these were FAT66 casing in my case).
I'm a bit of a tire freak - call it an obsession, although I'm better now, sort of ;-) I wore my Tiogas out, so am currently on an old favorite, Michelin Hot S 2.1 in back, and a WTB MotoRaptor 2.4 I had sitting around, up front. I had horrid probs with pinch flats on the MotoRap, but this one that WTB sent me as a replacement has been fine. But, they are definitely a hardpack tire - not quite as good in loose stuff. The Hot S is also a hardpack tire, but fairly light, and I've never pinch flatted one (even after NUMEROUS times of feeling rock hit rim - can't believe it hasn't pinched, and the casings are damn thin too!).
Anyway, right now what I'm hearing is good, at least for a front tire is the "new" IRC TrailBear. This is actually just their old Missle but with an XC casing, making it "light". Two guys I know love them. Doesn't look great for a rear tire though, although I generally find the Hot S is pretty good, so I could hang with that.
Others... The MutanoRaptors don't appeal to me much. Some folks love them, but look at the tread pattern - how can you get decent braking out of that? I'm pretty demanding of braking performance for tires. With disc brakes and how I ride, I like to be able to brake really late, and really hard, and expect the tire to keep up. WTB's don't do this in general, and the Mutanos look like they'd do it even less. Continental Vertical Protection 2.3's were fun to ride. They're really light for a "2.3" (they compare equivalently in size to the 2.1 Tiogas), and are very fast riding as well. But, braking is a little weak, and cornering could be better. I also had a lot of pinch flat probs with them, as they didn't feel good to me when pumped up past 30psi (apparently you need to run them about 35psi). But, depending on your terrain, and if you know to expect that they don't corner as well as say the Tiogas (few do though), they're really fun since they ride so fast, but still grip pretty well in the rocks and such. Panaracer Fire XC Pros. This is probably the area favorite, and a favorite by a lot of folks. It's just a great all around tire. The main reason I don't ride them is that I was wearing through them in literally a handful of rides (6 rides max, sometimes less). They're inexpensive and work well though, and many friends love them. I also prefer a little bit bigger tire.
As for the Tioga XC Extremes, ya, I dig these, but they too wear really fast. I've yet to try one as a rear tire. It wouldn't work as well as the Factory DH rear, which has a more rear specific pattern, but might still be fine (just a little less braking ability). But, as Jay said, they're really light, especially for their size, and they are relatively cheap. So, depending on whether I get excited for the TrailBear or not, these may be my choice. I previously ran one up front with a Hot S in back, and that seemed like a great combo for me. Note to some - the Hot S needs to be run at fairly low pressure when judging by a gauge. I tend to run them around 35psi. If you run them too high, they get more slippery in the corners in a much more exponential curve as the pressure goes up, as compared to other tires. But, run them too low and you'll get a rolling sensation (if you've ever rolled a tire, you know this will freak you out). So, spend a little time to find the sweet spot. Ok, I've rambled enough (see, I told you I was a tire freak).
