What are the subfields of chemistry that work very closely with biology?
In addition to jonsca's link of chemistry subfields, Wikipedia also has a list of biochem subfields. Find what research interests you, perhaps not based on a course you've taken. 

You can look up what professors are doing in their respective fields of research by visiting faculty research group sites online. Check out their publications, current projects, probably would be good to join a lab too. (I'm blindly assuming you're interested in research and/or graduate studies)

The list on Wikipedia first lists (for whatever reason these are "main branches" but I'm surprised biotech is categorized under "other branches"...):


Animal Biochemistry
Plant Biochemistry
Molecular Biology
Cell Biology
Metabolism
Immunology
Genetics
Enzymology


Getting into more or less random scopes of research topics which may or may not be within the above fields:


Biotechnology,
Bioluminescence,
Molecular chemistry,
Enzymatic Chemistry, 
Genetic engineering, 
Pharmaceuticals, 
Endocrinology, 
Hematology, 
Nutrition, 
Photosynthesis, 
Environmental Chem,
Toxicology
(Probably many, many others...)