Identifying whether amino acids are hydrophobic or hydrophillic
Does the side chain contain any Nitrogen (N), Oxygen (O), or Sulfur (S) atoms?  If it does, then chances are high that this particular R-group is polar (although it may not be charged).

The converse is also true, if the R-group lacks any of those three atoms then chances are high that the side chain is polar.  There are exceptions; Methionine has a Sulfur, but is quite hydrophobic (non-polar).  Tryptophan has a nitrogen but is non-polar.