Although it hasn't been mentioned yet, you should go look at the Acura TSX and TL. You get pretty much maximum gadgetry for a minimum cost (e.g., Bluetooth phone support, HomeLink garage door opener, heated memory seats, etc.). Pretty much the only options are color, transmission, and nav system. The TL is slightly larger, but comes with a beefy V6 rather than the TSX's arguable V4 (pretty good with the manual transmission, slightly underpowered with the automatic). Likewise, go have a look at the Honda Accord Coupe (available with a V6; essentially the same as the Acura TL, but there are no Acura coupes) and the Honda Civic Si (well within your budget; fast, fun car). I'm pretty sure the new ones have an appropriate aux-in.

Another manufacturer you need to investigate is Mazda. Again, lots of gadgetry, and several of their cars have a bitchin' fast turbo. I'd recommend against a Miata/MX-5. I rented one and drove it from L.A. to Santa Barbara and back. They're fun on twisty mountain roads, but the suspension is way too tight for freeway driving; it doesn't damp out the high-frequency road noise at all, so it will rattle your teeth.

Finally, a plug for Audi. The Audi A3 is one of these cars with a reasonable base price but a million options packages. Go play with their online configurator. The 2.0T engine should be faster than your current Mustang, and the 3.2 V6 should blow your Mustang away. More importantly, you can get Audi's DSG transmission. It's way better than any automatic transmission because it's got this cool dual-clutch setup. You might also want to look at some of the similar Volkswagen models, but I think the Audi has some nice luxury features you can't get from Volkswagen.