All Fabias and Roomsters get an auxillary socket as standard, as does the Octavia Elegance, 4x4, Scout and Laurin & Klement.
You'll need to buy dual-zone climate control to get one on the Octavia Ambiente or vRS, though, and that will cost you 590 or 450 respectively.
The base-level Octavia Classic and the entire Superb range don't have an auxillary socket either as standard or as a cost option.
The Aygo and Prius get an auxillary input as standard, so, you can simply plug in your iPod (using a 3.5mm jack lead) and effectively use the car's speakers as some large headphones.
The entire Toyota range (excluding the Aygo) can also be specced with an iPod Integration Kit'. It's compatible with all current generation iPod models that have an Apple dock connector, and will also work with many earlier iPods, although some functions might not be accessible.
The kit gives you an iPod connector in the glovebox. Simply plug in the iPod and a direct link is formed between the player and the audio system letting you select and play tracks using the controls on the audio head unit or (if fitted) the controls on the steering wheel.
The cost is 150 (plus fitting), which takes approximately an hour.
You can get an auxillary input socket on all but the most basic of Vauxhalls (i.e. Expression trim).
Some high-spec trim levels get one as standard, but otherwise you'll need a stereo upgrade, which costs from around 75.