Every so often a song will come along that really doesn't leave your brain for weeks. I find myself humming it at various points during the day and night and usually end up searching the radio or music channels for it. (Of course, in these days of quick downloads there is another way).
But it's rare for two such tunes to come along at the same time. But currently fighting for supremacy in my brain are Beyonce's Single Ladies and Lily Allen's The Fear. Both absolutely wonderful little slices of pop majesty. The Beyonce track has such a weird time signature all the way through and a great hook.
The Lily Allen song is equally good, more pop and straightforward than her last load of stuff to my ears. It's a standard Lily Allen structure though; talky, sweary verses and swooning, uplifting choruses. Really one to sing along to at volume.