Q: Topological K-theory references I am interesting in learning about (topological) K-theory. As far as I can see there are 3 main references used:
1) Atiyah's book:  This looks to be very readable and requires minimal pre-requesities. However, the big downside is there are no exercises
2) Allan Hatcher's online notes: If his Algebraic Topology book is any guide, this should be an excellent readable account of K-theory. I note that this is unfinished however.
3) Karoubi's Book: A nice looking book - perhaps less readable than Atiyah? (personal opinion, based on a quick scan)
Are there any other references/on-line notes available? I am probably leaning towards an Atiyah/Hatcher combination. 
(Can this be made community-wiki?)

A: "Complex Topological K-Theory" by Efton Park is a pretty decent introduction to topological K-Theory, but I'd actually go with Karoubi's book.
There is also a chapter on K-Theory in John Peter May's "A Concise Course in Algebraic Topology", which is in my opinion the best text on algebraic topology currently available, including some references and recommended further reading.
