A cheap and simple screen protector:
Tried it with one of my GPS units, and screen clarity was excellent with a brand-name clear tape (Scotch 3M), definitely worse with a generic brand. But with both brands, the tape peeled off without leaving any adhesive residue. I suspect it will be more prone to scratches than more expensive screen protectors, but rubbing it vigorously with my fingernail left no mark. Light use with a PDA stylus left minor but noticeable scratches; heavier pressure left more distinct marks. Seems to work fine with a resistive touch screen; probably won’t work well with a capacitance-based screen (e.g. iPhone and many other smart phones; any phone that supports multitouch).