And for holes, the diamond or carbide grit faced hole cutters designed for tiles, downside is that they are only available in a limited range of sizes.
If you are doing a lot, I really find the Excakt saw the best tool on thinner panels of all sorts of material, especially in situ.
I've had great success with a carborundum coated jig saw blade.
Available from Fibeglass suppliers not expensive and does not wear out.
Best to cover the FG with making tape or similar to prevent dirty marks if you are working on a finish surface,.
I use a dremel with a heavy duty cutting disc. I like some of the other replies though and would also consider them depending on the hole size and location.
Make sure you use the right type of dust mask. GRP dust is very fine and abrasive, so you do not want to breathe it in; it's probably the next best thing to asbestos!