The best buttercream frosting

Merrill has a great recipe on the site. Though, I generally prefer buttercreams that call fir some cream cheese, so not strictly a buttercream.

Rose Levy Beranbaum has lots of great recipes for meringue buttercreams (which she calls mousselines) in The Cake Bible.

Swiss and Italian Meringue buttercreams win the taste test every time. Swiss meringue boasts the advantage of avoiding a cooked sugar syrup and candy thermometer...instead, you simply whisk the sugar and egg whites over simmering water before beating to meringue stage in a standing mixer. Both varieties require cool room temperature butter added in small amounts to the cooled meringue until a thrilling silken cream magically develops. Flavors are limitless--- liqueurs, fruit curds, extracts, etc are easily added. These frostings are ethereal. Rich yet somehow light...they pipe beautifully and are sturdier than you'd expect...no confectioner's sugar grittiness. Truly sublime.