Most lower-end component speakers will fit, either 6 or 6.5". They normally come with 20mm tweeters which fit in the factory location, you just need to snap the lil holders off and fix them down with some double sided tape.
The woofers may be too big for the plastic speaker holders, but you can just hacksaw the plastic cover, so they will fit.
The other way you can go is get some 2-ways that have the tweeter and the woofer in one unit. One option that I know does work is the Pioneer TS-16xx series. They are 16cm speakers.
As far as models, well it's been a while since I've dealt with lower end speakers, but if you wanted to post up any options you are looking at, there are a few of us audiophiles who could say yay or nay.
Haha with my double sided tape and hacksawing I sound quite rangi, I assure you I'm not really that rangi