I've found that by just sitting down and clearing my head and forcing myself to think really hard, trying to connect the dots half-baked ideas and just mixing it up with random thoughts, I've gotten a whole lot better at thinking up of ideas. Patrick (patio11)'s article about his not understanding why people complain they can't find ideas really gave me a good kick in the side and motivated me to do this: http://www.kalzumeus.com/2010/03/20/running-a-software-busin... and I do find his comment about "walking in a store to find what people buy" a great starting point! I also have this book which I recommend 'A Whack on the Side of the Head' http://amzn.to/bm6vW4 which certainly did literally help me look at ideas in a different light and generate new ideas.
As a part of my effort to just find new opportunities, I've been documenting meta-algorithms to find algorithms (if a business idea/model is an algorithm). An entry I just added is:
* Learn a new concept, algorithm, (e.g. 'Programming Collective Intelligence' http://amzn.to/cMLnKj), and apply it to some problem in a different field (e.g. non-technical things in real life, or things I use such as Facebook, Twitter, etc). <-- An example of this: I read up on Shazam's clever algorithm and tried to use that method to solve something else.
Does anyone else collect such meta algorithms?
The classic book on creativity is "A Whack on the Side of the Head" by Roger Von Oech (http://www.amazon.com/Whack-Side-Head-More-Creative/dp/04464...). It is the book to read on creativity, along with his other book "A Kick in the Seat of the Pants"
His card decks (Creative Whack Pack, Innovative Whack Pack and Ancient Whacks of Heraclitus) are also very useful for breaking bad habits, generating ideas, divergent thinking etc. somewhat like Brian Eno's Oblique Strategies cards,which I recommend (http://www.rtqe.net/ObliqueStrategies/)
For more practical examples, exercises and inspiration, I like Creative Sparks (http://www.amazon.com/Creative-Sparks-Concepts-Exercises-Ing...) and Caffeine for the Creative Mind (http://www.amazon.com/Caffeine-Creative-Mind-Exercises-Brain...)
EDIT: I'd also recommend Organizing from the Right Side of the Brain "http://www.amazon.com/Organizing-Right-Side-Brain-Organized/... for tips on how creative types organize their workspaces. Handy if you're right brained, a pack rat, like "messy" workspaces or dislike the anal-retentiveness of Getting Things Done.
There's a section where he talks about thinking about other businesses or activities that are outside of your main focus, and after you go through that process you may come up with different ideas for your own business. It's pretty easy too. Just look around your room or where ever you are for objects and then think about how they are manufactured -- stuff like that.
I remember seeing a piece of lumber (I was reading outside) and it got me to think about how efficient some lumber manufacturers are. They might make 2x4s and other processed wood which they sell to retailers, but there's so much waste produced during the process in the form of sawdust and those manufacturers figured out how to sell their sawdust waste.
I never would have ever thought about something like that on my own, but it got me to think about how I can reduce waste and cross pollinate some of the things I create (code, blog posts, videos, etc.).
[0]: http://amzn.to/2CqmvqH (yes it's an Amazon affiliate link and no I don't care if you Google it instead. I just happened to have the link handy since I wrote about the book on my site in the past.)