One crossover I've thought of for Log Horizon is Sunstone - given that it's got a character who explicitly plays MMORPGs.
Another possibility is Assassination Classroom - neglecting your studies to play Elder Tales is exactly the kind of thing that's likely to get you into classroom 3-E - and teach you strategic and teamwork skills.
Another possibility is Assassination Classroom - neglecting your studies to play Elder Tales is exactly the kind of thing that's likely to get you into classroom 3-E - and teach you strategic and teamwork skills.