Books

Abair! faclair by R. W. Renton & J. A. MacDonald. Gairm Publications, reprinted by Clò Raghnaill. ISBN: 0-9551362-0-2 or 978-0-9551342-0-7. You can get it at Comhairle nan Leabhraichean. An excellent little beginner's dictionary, because it's both Gaelic-English and English-Gaelic, and also lists irregular forms, and the nouns in their different forms with the article. It doesn't include the pronunciation though.

The Gaelic-English Dictionary / Am Faclair Gàidhlig-Beurla by Colin Mark. Routledge. ISBN: 0-415-29761-3 (paperback edition). As the title says, it's Gaelic-English only. Like Abair! faclair, it doesn't include the pronunciation. It contains a lot of expressions though, and a grammar section in the back. You also get pointers for different orthographic variations of the same word. The layout is easy to read. Very long entries (especially of grammatical words) are set in boxes which improves readability, but it screws up the words on top of the page that indicate where you are.