Has to be 100mm. 80mm getting dropped by all the manufacturers, even World Cup riders switching finally.
I tried the DT Swiss forks XRC and if you can get over the price tag they are great. Really solid, light weight and performance is great. NOT for heavy riders though unless you go for the more heavy duty XMC 100 which is supposed to be brill. The lockout on the XRC is amazing.
SIDs are a great option, running an '09 one at the moment and no complaints. Loads of adjustment and lightweight. The remote lockout is not the best though.
I have heard bad things about '09 Rebas. Apparantly they have had reliability issues. The '08 fork was fantastic though and good deals to be had.
I ran a 100mm Durin last year and it was amazing. Really stiff, smooth buttery travel and bomb proof. I know Magura had reliability problems in the past but anything I have seen in the last year or two has been really solid.
Fox have a great reputation at the moment and certainly OC Tuning have upped the benefits now that they can be serviced here. James is a legend too. They are heavier, depends on what you want. '09 forks went on a diet though and are a little bit lighter than previous models.
So in short - they are all good
My choice - Durins or SIDs, DT Swiss if you can afford them. But that may change when I test the Fox's next month...