Silver Efex is well worth the money if you like black and white. About 30 rolls of Tri-x in money terms.


Bel Air by Mark Bowerman, on Flickr

If you want to save money, Snapseed gives you a good sample of Nik's effects for about $20.


Tide by Mark Bowerman, on Flickr

Like Chojin says raw files stand more post processing than jpegs.