Wolfgang's Vault has been a great resource for listening to streaming classic (and we mean "classic") rock and roll. Now they've added entire concerts to their features. You have to register on the site, but that's hassle-free. Try listening to this Jimi Hendrix 1968 concert at Winterland while you work. You'll either be energized or have an acid flashback. Either way, it's all good.
Jimi Hendrix Experience

Here's what Wolfgang's Vault has to say about this concert:

This run of Jimi Hendrix concerts at Winterland, with Dino Valenti and then Buddy Miles Express opening, produced some of the most interesting Hendrix sets ever recorded. In mid-1968, just as he was releasing his monumental Electric Ladyland LP, Hendrix began actively and fervently pursuing opportunities to jam with other musicians. He became more conscious of his improvisational abilities than at any other time in his too brief career. These shows capture Hendrix at his most exploratory, expanding the boundaries of his own playing and open to adding other musicians to the mix, in this case with no rehearsals.