The following languages/problems are decidable:

 1.  The set of encodings of DFAs which do not accept any string
 containing an odd number of 1s.

 2.  The set of strings of the form R#S where R and S are regular
 expressions and L(R) is a subset of L(S).

 3.  The set of encodings <G> where G is a context-free grammar
 with terminal alphabet {0,1} which generates some string over {1}.

 4.  The set of all Pascal programs P such that P does not halt in
 |P| steps, given an empty input file.

The following languages/problems are undecidable:

 1.  The set of encodings <G> where G is a context-free grammar
 with terminal alphabet {0,1} which generates all strings over {0,1}.

Here is an outline of the proof.  There exists a recursive function
that, given any <M>w, where <M> is the encoding of a TM, produces
an encoding <G> of a context-free grammar, such that L(G) is the
set of all strings which are not computations of M starting at w.
If M does not halt with input w, then L(G) consists of all strings,
because M has no computations starting at w.  (Recall that a
computation must end with a halting configuration.)  If M halts with
input w, then L(G) does not consist of all strings.

Thus, if we could decide whether L(G) contains all strings, we could
decide the halting problem.

 2.  The set of encodings <T> where T is a Turing Machines with tape

 alphabet {0,1} which halt given input <T>.