Last I heard (it's been about a year since I looked into numbers), Power/PPC chips appeared to be outselling x86 chips by a substantial margin with the caveat that it's hard to come by numbers from the "smaller" x86 vendors (like Via) that might very well be selling larger numbers than expected of the low end alternatives but at much lower prices and margins and so fly under the radar.
x86 is likely something like the 4th or 5th largest chip architecture by volume shipped today. Last estimate I've seen was in the 360 million range per year, maybe as high as 400 million.
That's after ARM, likely to ship 3 billion this year, MIPS and PPC probably in the 500+ million range each unless there's been massive unexpected changes over the last year.
X86 gets all the attention because it's on desktops and in laptops and because Intel is disproportionally important because their revenue is several times that of any other CPU manufacturer because nobody else ships nearly as many high end chips (e.g this puts Intel at 7 times Qualcomm, at second place, in revenue from CPU/MPU's last year: http://www.xbitlabs.com/news/cpu/display/20130521205843_Inte... )
And for the surprise contender, it is unclear where the 6502 architecture falls: It ships in "hundreds of millions" a year according to Western Design Centre). Note that this might very well largely be in the form of licenses for embedding the cores in custom ASICs or in FPGAs, so whether you'd want to count that is another matter (as an example, some Amiga's had keyboards with an embedded 6502 core + PROM and a tiny amount of RAM). It's possible that some of the other extremely low end 8-bit CPU cores that are still being used as micro-controllers might also ship volumes like that.
I've seen no indication that Sparc is anywhere in the running