As personal mixtapes and iPod playlists replace single-act CDs as fave formats, it helps to have good sources to cannibalize for your sets. This unusual Valentine's Day cover compilation comes from Hear, the folks behind the Artist's Choice series (mixtapes compiled by Johnny Cash, the Rolling Stones, and others), and it's full of surprises. There's Ron Sexsmith's swoony reading of the Bing Crosby standard ''Moonlight Becomes You'' and Nada Surf's shining take on Francoise Hardy's ''Au Fond du Reve Dore.'' The most wonderful track may be Iron & Wine's impossibly delicate version of the Marshall Tucker Band's ''Ab's Song.'' VALENTINE'S MIX MUST No sweetheart playlist would be complete without OutKast's ''Happy Valentine's Day.''