For anyone interested, these are the DLCs that are not part of the Gamersgate Magicka Collection (according to the list on Steam):

Holiday Spirit $1.00
Horror Props Item Pack $1.50
Lonely Island Cruise $1.00
The Stars Are Left $2.98

So it looks like a total of $12.47 for the game and all DLC available compared to Steam's current Collection price of $24.99 or ~50% off. Anyone know if Steam puts the collection on sale for less than that? I have had this one on my wishlist for quite a while.