One of my favourite collection must be the one from Kose Addiction: The Sand Castle edition
Perhaps I like this collection because it hints more towards summer than spring.
Moreover, the dusty, duny, sandy colours are so gorgeous. And I know Kose Addiction is stellar in making an excellent formula.
For more upcoming collections of new Spring collections I would advise to look at Rougedeluxe (here), who is always ahead of the newest releases.
I really like Bobbi Brown Rose Collection too, but for Addiction value I like the look of this one the most right now...
Ps: What is your ultimate spring 2012 lust-have item/collection?