The latest release is 4.72. This is a feature and bug fix release in the 4.xx series of releases - see the download pages. Documentation was updated for 4.71.
All versions of exim previous to version 4.x are now obsolete and everyone is very strongly recommended to upgrade to a current release.
The last 3.x release was 3.36. It is obsolete and should not be used.
There may be beta versions with available from the ftp sites in the Testing directory. Many people are using these without problems, but they are not recommended unless you are willing to work with beta software.