Im looking for something to upgrade my sound system inside the car.
I don't want something too expensive yet too cheap just around 100 for a set of 2 for the front and the same for the rear speakers.

What sizes will fit and which one will give me a better thump than the stock ones?
I got a sub and amp already.

If you want a better "thump" from your new front speakers, you're going to need an external amp to power them. You'll probably lose some of that low end "thump" when you get rid of the stock speakers if you run them off your head unit, it's just how things work. And for a better sound, look into getting a component set (a midrange, tweeter, and external crossover,) and a high pass crossover.

The best way to decide what you want is to go out and listen to as many speakers as you can; they all sound different to everyone.

6.5" will fit both front and back, but mounting plates will probably needed.

Some good inexpendive brands are CDT, Infinity, Boston, JL... and there are MANY others. It's all pretty much personal preference. But remember - you get what you pay for.

I bought a set of cdt's off my buddy, 6.5" and i amped them with a smaller pioneer amp, and they sound good. Your best off pairing some 6.5" speakers up with a sub as they dont provide with a whole lot of the lower db's.
everything mikew said is good advice.

Ok if u have $$$ and u want to get the best ****, get MBQuart Q-series speakers they are about 999$ per pair but dude, totally worth it. Right now I have the lowest model of MBquart which is MBQuart Discus but dude its way better then any sony, pioneer, kenwood car speakers on the market.
Go for either:
1) MbQuart
2) JL Audio
3) Infinity

Infinity Kappa 652.7i

a 7" Direct fit in for the front.

Infinity Kappa 62.7i

a 6.5" Direct Fit for the rear.

They sound really good for the price, this is just a genearl link for them, I am sure they get cheaper, but even powered off a Deck they sound really nice.

DTE

sepending on what you want....i have poineer 6 1/2's in the doors and 6 x 9's in the doors...nice clear sound

Some of the best bang for the buck.....I love the way Polk Audio sound. Very clear speakers and deliver a nice balanced, clear sound. If you want a little extra thump on a budget and have extra leads from your headunit, wire up a set of 6x9's onto your rear hatch lid. Increase the bass EQ gain on your headunit a little, and you should be very happy. Dustin and Manny both have this sort of setup, and its a great sounding setup that is good on space and the wallet.

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Well, for 4 speakers, I guess you could say you were planning on spending roughly 200 dollars. So I say, use that 200 dollars mainly on getting an external amp and front component speakers. You can leave you back speakers stock because your sub should be drowning out those speakers... So for 200 dollars, you could get a pretty good amp and speaker package. I say go for the Spr-17ls speakers from Alpine ( I have those) and maybe a kenwood amp that pushes 100 watt RMS in 2 channels at 4 ohms. You should be able to come away with around 200 dollars spent. That would be probably the best thing for you... Not to mention that the Spr-17ls speakers are probably one of the best you will hear.

As for me, I just got my speakers, subs, and amp and its ready to be installed. I will post the pics so you all can see in a little while!!!