The thing about springs over stock struts.... anything that's a different spring rate and/or a different length is going to wear out your stock dampers faster by requiring them to operate differently than they were designed.
Also, as the spring rate goes up, if your dampers aren't stiff enough you will become "over-sprung" and will hop all over the road like a ricer on cut springs (or me w/ my JICs
) Sometime, stiffer springs will also show you how soft the stock strut tops are, and the car may bounce on them.
All that said, lower and slightly stiffer springs can work well with stock struts. Lowering a car just .5" to 1" can really improve the handling by lowering the CG of the car. You may also see some aero benefit because less air will go under the car. Plus stiffer springs reduce body roll.
Don't forget, one option for suspension are STi takeoffs from Japan. For about twice the cost of springs alone, you can get low mileage struts off a JDM Spec C or Type RA! They will come with stiffer springs, matched dampers and the harder Group N top-mounts! (But they are "stock" setups, so they're not significantly lower than the stock US setups.) Check
www.gruppe-s.com. Max tends to get a few sets in from time to time. I was actually leaning heavily towards one of these setups, but eventually decided that I wanted the adjustability of aftermarket coilovers.
As for specific springs, I have no experience with them, since I knew I wanted to leave my stock struts intact (I wanted to just swap complete struts, and not need a spring compressor, plus I want to be able to put the stockers back on if I sell the car). Eibach, Prodrive, and STi pinks are all popular, IIRC. Try to find a set that don't lower the car extremely and are designed for the stock struts.