Transparencies
These are the transparent plastic films designed to be used with an overhead projector. Transparencies can be produced as easily as paper printouts, provided that your printer accepts suitable transparency film; most printers do. For colour overheads you will need a colour printer. While colour laser printers are frighteningly expensive, ink-jet printers are often perfectly adequate for this job. Interestingly, many inexpensive ink-jet printers that produce mediocre print on plain paper can produce strikingly good transparencies. Since most people only print transparencies occasionally, the fact that it might take half an hour to produce each sheet is not the problem that it would be for printing letters. However, twenty sheets at thirty minutes per sheet is ten hours, so be wary of leaving it until the day before your presentation before printing overheads on a cheap ink-jet printer. In any case, all printers invariably run out of ink when you try this.