When trying to start IPython in a virtualenv I kept getting the error
ImportError: No module named _sqlite3
I was using a python executable that I compiled myself, and it took me some time to realize that the compile process could find the sqlite header files but not the library itself. It turned out that on this machine (Ubuntu 11.04) the file libsqlite3.so is in /usr/lib/x86_64-linux-gnu, but python expected it in /usr/lib. Creating a softlink did the trick.