You could get an aftermarket muffler and have it welded in by a shop. That's what I did. The stock muffler is very heavy and good for scrap metal $$$.
You can't really just get a chip or an ECU reflash/whatever our domestic market calls it, Toyota has everything encrypted and the ECU is very "smart." It will do anything it can to get back to running just like stock, so the only way to change it is with an actual aftermarket ignition/fuel controlling computer, which is $300 for a boomslang harness (to make it plug and play), $200-3000 for the computer, and then $400-600 for dynotuning; additionally you have to find a shop that can dynotune and work with the computers usually used on Japanese cars.
Now, for real gains, you have to go forced induction. This is with a supercharger or turbocharger. That sort of thing runs $1000-6000, depending on your connections and you also still need an aftermarket computer. You cannot run F/I with the stock ECU because it's based in a very narrow set of parameters and will probably blow the engine trying to run the way it was designed to.
If you want to get more power, speed, and handling, you either need to be willing/able to shell out the $$$ to modify a car with little aftermarket support, or get something different. I'm not trying to be an arsenic, but Toyota is pretty good at maxing what they build out so there's not much to improve on. Except the 1ZZ header, that thing is....well...
You see.
Or just make due and enjoy what you have, because what you've got is a loyal steed who will unlikely ever let you down so long as you take care of it. Then you can drive past all the other guys broken down on the side of the road and LOL all the way past them.
"If you don't love me at my diddliest, you don't deserve me at my doodliest." - User ktluvscricket of reddit