springs by themselves are not worth doing IMO. YOu need to do springs and struts at the same time. THere are a wide variety of springs out there. I got mine on sale from www.bavauto.com
. They are working great for me, however I have heard that they have a tendancy to sag over time. For shocks, Bilsten sports are the favorite for lowered cars.
In the end it really depends on if you want thte look or the performance. If you just want the look you can shave some money off by going with lesser quaity brands. But if you want the car to be able to perform better (not worse than stock as it would with lesser brands) then you will have to stick with Bilstein shocks, or maybe Koni Adjustables and bavauto springs or H&R if you do not might extreme camber problems. I can't remember which other companies are good right now.