Looking for something cheap and effective, which would you suggest. So far I have a headunit and front door speakers. What could I do for more bass and sound in general?

2- 6X9s in boxes with an amp?
Bazooka Basstube?

 

A good, single 10" sub can make a world of difference. But you can also go with the Bazooka tube, or something like the Infinty Basslink. Another option would be to get a couple dedicated midbass (6.5", or 8"..if you don't mind some cutting or bending) ran off an amp.

 

Wow, there are SO many ranges of 'good cheap' sounds. For me, i just added my alpine head unit to my car and swapped over my boston acoustics from old car as front speakers and had a pair of ebay'd Legacy brand generic xplod looking speakers into the rear and the sounds are 'decent'. Far superior to stock. The only thing i really lack is good bass which in my last car i had a cheap $25 dollar 'tube' with a built in amp that i got for free. Didnt add a ton of bass, just enough to hit harder then the speakers without an amp. My alpine unit doesnt put out enough power to push the bass out on the speakers in my car. I say throw in a 10" or zook like mentioned and add tweeters to replace the factory ones.