Let's start with examples from Germany: Here, a popular post-paid model is a fair use all you can eat plan with a volume cap, for example 5 GB, after which the bandwidth is throttled down to 64 kbit/s for the rest of the month. While staying within the bucket, speed is only limited by the device, network capability and radio conditions. Prices for such plans range between €30 and €40. Other volume caps also exist.
In the pre-paid sector, there are many offers for small screen devices billed per MB. Prices range between 20 to 40 euro cents per MB. Great for low to medium use with OperaMini and e-mail without attachment download. Some operators are also offering prepaid plans for notebooks with volume caps of a couple of hundred MB to a couple of GB for prices anywhere between €20 and €40. Vodafone and others have offers based on time, for example 24h access for €5 and a week for €10 with a volume cap at 1GB. If you dig a bit deeper the weekly package can also be had from a reseller for €6.99.
Finland: Here, Saunalathi Saunalahti offers unlimited bundles and charges based on maximum throughput. Prices range from €9.80 with a speed cap of 384 kbit/s up to €34.90 for a throughput of up to 5 MBit/s Gbit/s.
Austria: The el dorado land when it comes to mobile. Drei (Hutchison 3) sells 15 gigabytes a month for €15on a postpaid contract. Prepaid contracts are available as well, like for example those of Mobilkom and One, where €20 buy one gigabyte that can be used over 12 months. Maybe not very attractive from a price per GB point of view but for occasional users it's an unbeatable monthly price.
France: Here, clocks are still ticking differently compared to pretty much the rest of Europe. Orange for example offers 1 GB of traffic on a post-paid basis for €39.90 after which the bandwidth is throttled. 4 GB are offered for €79.90. Prepaid packages are only available on a time basis. 20 minutes go away for €3, an hour can be had for €8, six hours cost €25 and if you want to be connected for 12 hours over the duration of one month, you have to invest a staggering €35. Nothing really for always on connectivity fans.
Feel free to add to the list if you know of yet another variation.