As Donovan mentioned, the Ring (Nordschleife esp) is the jewel in the crown (I am planning to be there first weekend in October incidentally). Outside Germany, you can find opportunities to drive on most circuits - I have done Spa-Francochamps with a Porsche club; in the rain, a very tricky track, but the downhill section past the old pits and up to "eau Rouge" is a unique experience -- nothing like it anywhere in the world. The key sections of Spa can also be experienced as a public road but since traffic is both ways, you won't be able to take the racing line!
In France you can find a directory of tracks and events on http://www.pilotedudimanche.net/
(literally "sunday driver"!). There are frequent events at the circuit at Mans (self-drive but also you can rent prepped cars). Very nice track with lots of run off (gravel). There is also an amazing pro-level karting track nearby. You can also drive some sections of the public road portion of the circuit -- including Hunaudières, the long straight (also called the Mulsanne because of the turn at the end), that used to see 240mph+ runs by the P-917s.
There are a couple of smaller tracks near Paris and there are small companies that run weekend self-drive events. I am partial to just one because the people they register tend to be calmer than others, so less chance to have stupidity on the track. Rules are slightly different to the US but they always have a driver's meeting to start off. Some nice cars usually show up - had some Atoms the last time...freakin unbelievable acceleration and grip.
Zolder in NLs is a decent track too -- its been several years since I was there but they had friday at the track kind of events back then.
And if you can get to the Isle of Man...that is a whole island worth of track basically.