Taye Taiwo of Marseille is a free agent in the summer. I'd be happy for the club to acquire him, he's a heavily-built, and somewhat offensive, left-back, but I'm sure he could adapt to play left CB. A defence next year of Sagna, Eboue, Djourou, Koscielny, Vermaelen, Taiwo, Gibbs and Clichy, in front of Sczezney/Fabianski, would be most satisfactory.
Problem is, he wouldn't necessarily be guaranteed first-team football (unless he displaces Clichy, which would be a possibility). He's professed a desire for AC Milan, and he'd immediatly slot into that team considering their poor selection of left-backs.