The song featured in Grand Theft Auto V is the title track on the 1968 album called Ogdens' Nut Gone Flake by the British band The Small Faces. You can listen to it right here. (Or watch the trailer.)
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One of my top-5 all-time favorite bands. I freaked out when I heard them in the trailer. Anyone who likes 60's rock owes it to themselves to check out a best-of (at least!).