First and foremost, the previous posters are totally correct about safety as a potential issue here. Second, effervescence and explosions are two quite different things. It sounds like what you are actually looking for are reactions that produce a fairly large amount of gas quickly. There are a number of common household ways to do this, some safer than others. In order to be safe, you should always work in a shatterproof container with a wide opening. NEVER use a closed or narrow necked container; gases can build up large pressure quickly, and even a plastic container can become a dangerous device. Also, be prepared for a mess. When I do soda and Mentos "fountains" with a class, we do it outdoors and then hose down the area.
Here are some things that you can try, following the safety precautions above:
Baking soda + any acid (vinegar, lemon juice, soda) - this can be made more effervescent by adding a squirt of dishwashing soap to the acid before mixing with the baking soda
Alka Seltzer tablets are fun; if you add soap to the water before you drop the tablets in, you get a lot more foam.
You can make your own fizzy "bath bombs" by mixing baking soda and citric acid granules with scented oil; see the instructions here.
There's a really neat variation on the baking soda and vinegar routine here. It's more work, but unique.
And, here is a link to instructions to make a chemical reaction that creates a "lava lamp" effect in a bottle. Easy and fun.
Have fun, and BE SAFE!
I agree with post #2 completely. You never want to underestimate the power of chemicals or chemistry in general. Some of the most common household ingredients could result in really dangerous combinations. I would not want to be liable in this situation if you accidentally blew yourself up.