Things I would definitely recommend for a reel are: fire, water and dust. Those things are used everywhere in pretty much every game, from in your face like a car crashing through a wall, to super subtle like a character’s foot impacts on the ground or gently falling from the ceiling.
For combat oriented stuff, I would say weapon trails/slashes and quick, flashy impacts are the bread and butter there. Check out everyone’s threads for the Trails challenge on here for some good stuff on those. Be able to break your effects up to create looping versions. A good example is the Barbarian’s Whirlwind attack in Diablo. You’ll need a particle system for the windup, one that can convincingly loop for as long as needed, and one for the finish that can convincingly overlap with the loop when it’s canceled early.
As for tutorials that have helped me the most, Jeremy Baldwin’s Visual FX Masterclass is a mountain of quality fx info; worth every penny and more. It looks like Eat3d shut down, but it seems like you can get the tutorials here http://www.cgriver.com/7546-advanced-vfx-masterclass-bundle.html . The price might seem like a bit much, but I can almost guarantee you, you’ll get more out of that than a semester on vfx at any school currently.
If you still want more focused education on Houdini, then I’d recommend signing up for a mentorship. They will run you about the cost of a 18 unit school semester, but you will be getting focused training and 1 on 1 time with a game or cinematic industry professional who uses the program to a high level with lots of experience.
Edit: just stumbled upon this http://www.appliedhoudini.com/