Rosalind is a great way to pick up some bio along with your algorithms.
The instructors also created a course on Coursera called "Bioinformatics Algorithms" that I highly recommend. It's basically an ordered set of rosalind problems but accompanied by a textbook and lectures. It was one of the most interesting things I did last year.
Agreed - it's one of the most enjoyable Coursera courses I've taken. Part Two starts February 16th. [1]
To expand a bit, what I liked about the course was the textbook, algorithms and their practical application in a non-CS field with a good set of programming problems that are automatically assessed.
Also suitable for learning new languages (and bioinformatics).
The implementation of the site is awesome.