Each tier grants special bonuses and benefits; some bonuses include a 10% store discount, RuneCoins, beta access, and armor. The gold package also grants all 2012 promotional items. The bronze package gives three months of membership for $21.95, the silver is six months for $39.95, and the gold lasts 12 months and costs $74.95.
If you want to get your hands on one of these packages, you'll have to act fast. Players must subscribe to RuneScape between December 20, 2012 and January 31, 2013 in order to take advantage of this offer. For more details, check out the official FAQ.
[Source: Jagex press release]