i do both advanced english and chemistry. english isn't as much work as everyone makes out, and advanced is only a little bit more work than standard, so its worth it.
chemistry i find difficult, but its also worth it. it scales well and obviously you're good at maths if you're thinking of 3unit, so you'll have no trouble with the calculations.
my sister loves biology. my friend says business is a bit of a bludge (which would give you a bit of a break =]).
lots of unis only require you to do english, maths and a science, so you'll be able to do nearly anything!