Looking for good mid-high range speakers?

I currently have an amp and aftermarket hu putting about 90w rms to my 6.5" doors and my 6x8" rears. I'm really short on cash, so i'm thinking about maybe getting a box speaker for the rears and just putting it on the floor. in the back i have a 400w 10" sub for the b. i'm open for any kind of suggestions, thanks a lot for your help