Biological Macromolecule Crystallization Database
The biological macromolecule crystallization database (BMCD) compiles, crystal data and crystallization conditions from literature. The database is as simple to use as Google. However, I find that I need to use the Advanced search to help narrow down the results. The advanced search options are shown:

I previously wrote about the cryoprotection database (cryo database) and thought it would be interesting to compare them:
Which database is larger?
Cryo:1,777 entries
BMCD: 14,372 entries
Which database extracts the best crystal and crystallization information?
If you are looking for general information about protein crystallization, then the BMCD is by far better. However, the cryo database is helpful if you are looking for that specific information.
An issue I came across when using the cryo database was that it did not list the PDB identification code. This would save users from having to look it up in the original reference. My guess is that the user base of this database is mostly crystallographers so a PDB ID would be helpful.