I haven't completely run out of them yet, but UD Sin, Toasted, and Y2K are all close to pan. I wear them so often I can't imagine not repurchasing, especially since they're available as singles now.
Honestly I have SO MANY shadows that I don't hit pan on them very often... but MAC Satin Taupe I am running out of and can't find a replacement in my stash that I love.
And Laura Mercier African Violet - I got this in the Artist Palette at Christmas and OMG, I love this color. I feel the need to buy multiples to have just in case. :-P
Do you have MAC Mulch? Its a good replacement for Satin Taupe.
MAC Club- Ive got this in a palette and on its own. Its my fav regular line color. Loved MAC Mod but they discontinued that years ago and they have yet to come out with a replacement.
I'm about to run out of my Lorac Pewter and it has been discontinued as a single color (can be found in a palette). UD Pistol is a good dupe though so I'll finish up the Pewter, then use and re-buy Pistol.
I'm also about to hit pan on UD Virgin, Sin and Toasted.
Mac Brule, Blanc type, grain, and all that glitters. I think I've bought brule at least 3 times. Takes me at least a year of pretty regular use to go through one though so I've been buying these for years.
MAC Retrospeck. It's a shimmery light gold. I'm blond, green eyes, black eyebrows/eyelashes, and medium skin with red undertones, and light gold is where it's at for me as a neutral.