BMW Clubs and Porsche clubs hold track events just about everywhere. Also lots of private party companies that host track days. some with instruction and some not. Then you have the manufacturers that have their own training at several of the circuits here.
I would say for any track nut the pinnacle is a private training day at the Nordschleife. The public tourist laps are way too popular, crowded, and dangerous to get much value out of it. A local BMW club that partners with BMW CCA has an international school at the Nurburgring every August. This school is 4 days long. only 80 cars in attendance. the entire track is closed for the school. Its split up into 11 sections and you really get a chance to learn each piece. Complete laps (continuous) are done in the afternoons. At the end of the school, you go out for your graded lap. Just you and the Green Hell all alone. What an erie feeling! By far the best DE I have ever participated in. If you want a list of companies and orgs hosting track days PM me and I'll provide you my list.
"It gave you amazing satisfaction, but anyone who says he loved it is either a liar or he wasn't going fast enough." - Jackie Stewart on racing at the Nurburgring