Use a candle stub attached to a meter stick as an igniter. After several practice runs you should be able to use the lighter to catch the bubbles and light them. Turning off the lights will enhance the effect. This can be used to show combustion, detail the properties of a common gas, produce an equation for balancing, encourage observation, introduce a discussion of fossil fuels, and ignite other discussions. Your students can tell that methane is a gas, has a density less than air, is flammable, and is not very soluble.
Safety is a concern with combustible reactions.
The bubbles burn with an expanding ball of fire. Be sure that the bubbles are well away from you, your students, and the funnel before lighting. Only experienced and trained personnel in safety and chemistry should perform this demonstration. Appropriate safety protection and procedures should be followed at all times. Bassam Shakhashiri Chemical Demonstrations Volume 1 University of Wisconsin Press Madison, WI 1983.