We've got the extension library full of great stuff. Notably, lately, the fabulous pagination extension that makes "no page number on first page" so easy.
Envelopes are something else that I get a lot of questions on.
Is anyone out there working on making envelopes easier with a nice extension? I've been told that the approach to envelopes used in Corel WordPerfect is a good, simple approach.
If there's something out there already, or if anyone's going to write something, let me know when it's done and I'll shout it from the virtual rooftops!