TV, radio interview...
Role play and drama can really help children to express their ideas in science.
Why not have one child play the role of an interviewer and record a discussion with a group of children who are 'scientists'? Topics could include environmental issues, pollution, safety in science as well as getting them to explain scientific principles.
These days it's really easy to record using a PC, but it is best to use a separate microphone so it can be positioned carefully. Video recording is also very easy now, and simple camcorders can be used to make short films. Try the equipment first as there is nothing worse than taking time to do an interview only to find nothing has recorded!
If you are really ambitious, many computers now come equipped with video and audio editing software for really slick productions.