Thanks, this helped a lot... I'm leaning towards inifinitis lol
Having Infinity speakers in my 98 4Runner, I hope I can give you some good feedback.
Every speaker has a peak wattage and an RMS wattage number, I'm sure you've seen them. The peak wattage doesn't help a whole lot, unless you've got a powerful amp powering your speakers. The 4Runner stock amp is... not so powerful so we'll ignore that number. The RMS is the consistent power rating it can handle and not have any distortion. You'll want to match this number close to where your amp is rated at (also in RMS wattage).
Most infinities are rated at 60 RMS and higher, some a little bit lower, and their Kappa line significantly higher. These speakers are made to be paired with a high powered amp to produce good, clean sound. Our 4Runner amp I think is around 15 RMS, pretty low. Most aftermarket head units will have a built-in amp of 20 RMS or so, which is still very low. Being so underpowered, the $100 infinities will sound a whole lot like the $20 paper speakers that were in it before.
How do I know? I installed my Infinitiy speakers and amp in stages. When I had changed only the speakers I was underwhelmed at how they sounded. My front speakers had not blown and they sounded just like the paper and foam Toyota speakers that I had just replaced. It would have been a complete waste of money if I stopped there. Then I added a new head unit and an amp and they came to life! Couldn't be happier on how it turned out.
I recommend heading down to your nearest Best Buy, Fry's, or other regional audio store and listening to a few speakers that are NOT powered by an amp. You'll notice a few you like that will be more in the $40-$50 range that will work great for what you are looking to do, just a direct swap of speakers. For this sort of purchase, brand won't matter very much. What does matter is what YOU think sounds good, it is your 4Runner after all! Just watch out... some audio tech might try and sell you on more expensive speakers, amps, subwoofers etc. so just know what you want and are willing to spend before you go in!
You might find my 3rd Gen audio thread helpful:
http://www.toyota-4runner.org/3rd-gen-t4rs/203866-thinking-about-upgrading-your-sound-system-do.html