As a minimum you should have the Ordnance Survey 1:50,000 scale Landranger Map for North Skye (Sheet 23), or for South Skye (Sheet 32) or both, depending on where you are planning to explore.

If you are going to venture off the main paths (and there are many areas with no paths at all), then the more detailed OS 1:25,000 scale Explorer Maps are a good investment. The areas covered are:

Dunvegan - Sheet 407
Trotternish - Sheet 408
Portree & Bracadale - Sheet 410
Cuillin Hills - Sheet 411
Sleat - Sheet 412

All OS maps are available on paper or a weatherproof finish. If you plan to use a Skye map more than once, the latter is a good idea!

 For serious walking and climbing on the Trotternish Ridge or in the Cuillin, consider investing in one or both of the excellent Harvey Superwalker sheets for Skye.