Gail is pretty awesome-sauce. Some of my favorites of hers are:

Don't Give Your Heart (long, but good) - Ethan leaves Giles trapped in his own mind, can Buffy help him escape?

Tomorrows - Epilogue to "The Prom".

Then there's Watcher's Retreat by Rari Coss (another long fic, but good)- Giles finally gets to go to a Watcher's retreat... but something is amiss.

and Matched Set by Koala - Buffy and Giles become the hunted.

And if you want to search for yourself, buffygiles.net is the home for most of the B/G on the web.