I know SCAMPER & Ideo cards, but I'm curious if there are any other important techniques/methodologies one must not miss. I'm particularly interested in those that you would resort to use for a client's project.
well you can also try applying AGILE coding principles too. it has worked great for us.
Whether you are creating pixels or coding.. its basically the same thing. Up until the last few years..the software industry has for many years been building things in a linear fashion, ie generate a HUGE spec ( usually based on a lot of assumptions ) and then build that HUGE project in a linear fashion. This process no longer works because it is $$ + doesn't allow for agile changes to external market forces.
Enter AGILE. Dont build the full house from the bottom up. Build a room first. invite people to test it..then take notes, then add another room.. or not cause u may find out you need to build a loft. Stay light and flexible so that you can easily make modular changes to what you are building. This allows for random inspirational ideas to take fruition and keeps your client happy. *This methodology only works using Time&Materials. So your challenge here is to convince your client that this will SAVE them $ in the long run, and produce a higher quality product.
We always use this technique when we are building a brand or animation for a client. It allows the client to have an early stake in the discovery/creative process and throughout the lifecycle of the project.