We're in the thick of it now: full-on tourist season is here, and while you may be fighting your way through thicker lunchtime throngs than ever, elbowing open London guidebooks and tube maps out of your way at every corner, we've got a round-up of decidedly non-touristy and inexpensive fun to be had this week. Monday: Free in-store gigs, hath sweeter words ever been written? The HMV on Oxford Street tonight is featuring a......