I also compared the A4 1.8 with the 325i for a couple of months before I decided to go with BMW. Both are nice cars, so it was a tough choice for me.
Like the other poster said, Audi's interior is second to none. When driving at night, it's like a jumbo jet cockpit with all the interior lights on (even the inside door handle). Their options are also cheaper. Audi has more storage space; bigger glove box, and storage bin under both driver and passenger's seat.
I picked BMW mainly because it just feel right sitting inside. I felt so trapped when sitting in the Audi even though it is bigger than the 325 on paper. Audi's free maintenance covers 4 years vs. 3 years with BMW.