Coldplay’s ‘42’ from Viva la Vida or Death and All His Friends (starting about 1:45), Nine Inch Nails ‘Complication’ from The Fragile.

Update: Fleet Foxes ‘Quiet Houses’ does this even more.

\def \newpi{{\pi\mskip -7.8 mu \pi}}

This, when rendered by pdfLaTeX, gives:

Zoomed in, we can see the problems with the symbol. I propose instead that the symbol defined as this should be used:

\newcommand{\cak}{\mathring\pi}

This symbol (rendered here in Zapf’s Euler) displays nicely the idea of pi as a full circle—and it has a nice tie-in with ancient mathematics: Diophantus used M̊ (an M with a ring above it) to represent the unit term in polynomial equations… we can think of pi as the ‘unit’ of angle.

Oh, and the name ‘cak’ is due to apotheon on Reddit, because:

As pi is to pie, so cak is to cake. Cakes are usually somewhere around twice as big as pies (in terms of height/volume), too.