First of all, what size rims have you got? Have you rolled the guards at all?
I would steer away from cheap coilovers, I have personally seen 3 coilovers struts fail when pushed moderately. Cheap being less than $800 per set.
A good set of coilovers will set you back around $1200-1300, offer adjustable damping, adjustable camber, really easy adjustment of ride height, and sweet handling characteristics.
IF you don't want to spend that sort of cash, or wish to stay with lowering springs and struts, read on.
To retain some sort of nice handling characteristics, you would need to run a "short stroke strut" when using springs that give more than 20mm of drop. Otherwise the struts will be almost at full compression, and they will hit the limits of their travel on medium bumps. Just remember that the lower you go, the less suspension travel you are going to have.
Avoid King Springs and Pedders like the plague if you wish for a nice handling car. They don't lower the corners evenly, with the heights being up to 10-15mm out on each corner.
Decent spring brands are the likes of; TRD (hard to get is most cases), IMAC, Eibach, Tanabe Springs, Koni. A full set will end up costing around $450-500 including postage.
Decent shocks include brands like; Tokico, Koni, Bilstein, and KYB. A full set will normally cost upwards of $500.
Almost all of the shock/spring manufacturers above have proven themselves in street/track setups.
A decent spring/shock combo will see you getting into coilover prices anyway.
Do it once, and do it right. Otherwise it isn't worth doing and will probably be a serious risk to your life.
My 2c.