I bought some new tires for my 328i a few weeks ago.
I've had lots of good luck with Michelin tires over the years, but doing some research this time showed me that the Michelins that I liked were going to be $160 per tire. That's a fair bit of money for tires.
I spent some time at TireRack.com reading the reviews, and ended up choosing a set of Yokohama V4s tires for $104 a tire. After a few weeks on them, I'm pretty happy. They're grippy in both the wet and the dry and you can feel when you're about to lose traction. They're reasonably quiet on the freeway - not quite as quiet as I'd hoped, but the 3-series isn't designed to be a super-quiet car.
I got them from Discount Tire, who gave me really nice service. They were cheaper and had more selection than Costco.