If you're taking the train in Germany and adjacent countries, purchasing a BahnCard can give you additional discounts on ticket prices. You can either get a BahnCard25 (for 25% discount on tickets) or a BahnCard 50 (for 50% discount). And they are valid for a full year.
However, be aware that these discount cards are sold as subscriptions. That means, if you do not send in a written cancellation within 3 month before the end of the year, you will automatically be charged for a second year!
This is exactly what happened to my daughter after she spend quite a bit of time travelling through Germany last year. She just got a new card in the mail and got billed for it. Another lesson learned and now it's crucial to send the letter out so she doesn't get billed for a third year ...