Just looking through HMV Digital for a few tunes, but notices a few glitches, with some tracks having additional tracks attatched which, if brought with the top 40 track, become free. Extra Tracks Worth 79p or 99p For Free.
All Time Low by The Wanted, Also has free Remix version (worth 99p)
California Gurls by Katy Perry feat. Snoop Dog, With Hot N Cold Remix (worth 99p)
Bang Bang Bang by Mark Ronson, With Remix (worth 79p)
We No Speak Americano by Yolanda Be Cool, With 6 Remixes (worth £4.74)
Just Be Good To Green by Professor Green Feat. Lily Allen, With 3 Mixes (worth £2.97)
Always nice to have a bit extra for nothing!
I'm sure there are more, just need to have a look, will update when i find some more