I use the Zaino tire stuff. It comes in a squeeze bottle, and you just squeeze some onto a rag or sponge. It doesn't have that cheap looking super glossy appearance of Tire Wet and all that other spray can junk, plus it's not silicone based like all of those so it doesn't turn brown. Best of all, it doesn't sling crap all over your paint. It gives a satin appearance that I think is much more tasteful than the gloss appearance, but gives a much deeper black look compared to untreated tires.
www.zainobros.com