First off, let me say that Scionlife.com is a HUGE bank of knowledge about Scions. You might sign up and start reading there.
Second, the companies making turbo's are
Dezod -
www.dezod.com
* Stage 1 turbo
Zero Point Industries (ZPI) -
www.zeropointindustries.net
* Stage 0 & STage 1 Turbo
* They also make a S/C Pully for added boost on the TRD supercharger
Scionspeed - Unsure of their different stages
* it should be noted a LOT of people have had problems getting turbo's from these guys, or, after waiting months, getting their money back. Not even sure if they advertise a turbo on their site anymore.
http://www.scionspeed.com
Sound Performance -
www.sound-performance.com
* Currently developing a turbo, looks great, check out their threads on scionlife.com about the process.
http://www.scionlife.com/forums/viewtopic.php?t=94995
Turbonetics -
www.turboneticsinc.com
* May not be on their web page yet. Again, lots of information at Scionlife.com
It should be noted both ZPI and another compant NST (Non-Stop Tuning) both make supercharger pullies I believe. I know that NST makes underdrive pullies to free up power at the crank. If you explore the crank pully route in any regard, Please take some serious time to educate yourself on the problems associated with our car's design and lightweight crank pullies. A member of Scionlife.com and Yoursciontc.com, Lo_bux_racer, explaines the long-term damage inevitable from running these pullies.
I rarely read this forum, so, if you have a question you can find me on Scionlife.com.
http://www.dezod.com/pd_dezod_motorsports_stage.cfm