Catalytic Site Atlas
The catalytic site atlas (CSA) is a database that displays active sites and catalytic residues of enzymes (ref). The database is regularly maintained, but has not been updated since August of this year. The database currently contains 25,537 entries based on 968 literature references.
The site has a number of search options (located at the top of their page) that include PDB, Swiss-Prot code and EC number.
Below is an example of some of the results that are produced by the CSA. The catalytic residue in this case is an aspartate located at position 93. I would like to see the catalytic residues highlighted differently so that they are can be identified quickly.
The CSA also performs a homology search using Psi-BLAST. This information is very helpful if you are looking for evolutionary relationships between proteins (ref).
The CSA help page is really good (although a number of links to it are dead) if you would like more information or are having trouble interpreting the results.