Reflashing the ECU on the Toyota 1ZZFE or 2ZZGE engines will probably not net you any appreciable performance gains - but will allow you to get stuff like the OEM security system or logic controls in the various electronic bits to work correctly.
Older Toyotas can be reprogrammed - but not by any of the vendors you mentioned. Couple of guys in the UK were doing it for awhile - but the market hasn't really turned up on these Toyotas. Basically it entails pulling the ROM off the OEM chip and copying onto separate Flash ROM - and tweak it from there.
For the WRXs and EVOs - being turbocharged and a strong market for user tuneable engine computers - much easier to get better performance curves playing around with air/fuel mix, boost, and ignition timing.
Unfortunately, Toyotas are not as easy to play around with as others manufacturers. Good Luck.