According to Consumer Reports Buyers Guide, the 2005 3 series are reliable vehicles. However, to get features like Bluetooth and MP3, they were first available on the 2006 model.
I just purchased a 2006 325Ci convertible with sport package, premium package, and navigation for $30K. It's a CPO vehicle with 19K miles. As you probably know, that means I have two years of factory warranty which includes all the maintenance. On top of that, I have two more years of CPO warranty (6 years or 100,000 miles. At the dealership, I was offered maintenance to cover that last two years for about $2000. Given the cost of BMW maintenance, it's probably a good move. I have read in other forums that you should only buy these extended maintenance contracts from the vehicle manufacturer.
You can have an iPod adapter installed on the 2006. I've searched for one on the web, but so far haven't found any alternatives to a BMW dealership. To integrate it with navigation is $845 installed. Without navigation, it's $383. Those prices came from the BMW USA web site (www.bmwusa.com), which provides links to my local dealership so I can get the costs for my area.
You can also search for CPO vehicles on that site. That's how I found mine. I live in San Diego, but I found the car at a dealership in the Bay area.
I test drove the 2007 328i convertible, but didn't feel it was worth the $7K difference. My two year old vehicle is like new, and I'm completely satisfied with it.