The most recent stable version of Xen Tools is 4.9.1 and you can download it via the following link:
A detailed change log can be found in NEWS.markdown in the source tar ball.
GPG signatures of releases 4.2 to 4.5 may be validated using Axel's 1024-bits public key.
GPG signatures of releases 4.6 and later may be validated using Axel's 4096-bits public key.
Binary packages of xen-tools are also included in the Debian GNU/Linux Project.
These releases are just listed for historic reasons:
GPG signatures of releases until 4.1 may be validated using Steve's public key.
The release which you can download above contains a full changelog which is automatically generated from the git repository.