Two sections of this site will be interesting for you grammar-wise. Beagan Gràmair - A Bit of Grammar - Explains how the pronunciation works, and covers some important grammar points. Some of it is written in a humorous way, so it's actually quite fun to read. It uses the IPA for pronunciation, which might look a bit complicated in the beginning. Don't let it put you off, you only need to learn to recognize the symbols used for Gaelic, and not the whole alphabet. It's the only way to get an exact transcription of the sounds. Fuaimean na Gàidhlig - The Sounds of Gaelic - Here you can fill the IPA symbols with life and listen to MP3s.

This is not a grammar page per se, but an online course. Still, it is pretty grammar oriented, so you can use it as a grammar resource as well. If you have problems with their programming, here's a direct link to the lessons.

Colin Mark's Gaelic tip of the week. He explains how to find the right expressions for what you want to say, so you won't be speaking Beurlig.

Si tu es francophone, cette page donne des éxplications, surtout les verbes. C' est pas complet, mais c' est util peut-être: Les règles de prononciation du Gaélique; Les verbes "être", "avoir" et la conjugaison au présent; Les possessifs et les numéraux; Petit lexique de mots et phrases courants; Correspondance entre le Gàidhlig et le Gaeilge.