I'm trying to learn how to use ArcMap.
I would like to find some example MXD files for ArcMap, but couldn't find anything googling.
Does anyone know where I can find any MXD samples for ArcGIS 10?
If you want to learn ArcMap I think searching its online help for tutorials will be your best starting point.
An MXD file on its own does not contain spatial data so a search for map packages *.mpk (MXD + spatial data) may prove more productive.
Another great way to learn the software that many users are unaware of is to use ArcTutor (a set of tutorials with .mxd docs, GIS data, and tools) which is available for free for anyone who has obtained ArcGIS Desktop. Unfortunately, you can download only some parts of ArcTutor on ArcGIS.com; most of the tutorials are available only via Esri Customer Care Portal which you as an Esri customer should have access to.
Esri Training should also be a main entry point for anyone learning about Esri GIS technology. There are dozens of free web courses with the access to the training data (.mxd map documents, geodatabases, and tools). The tutorials are updated regularly and include the latest software versions.
Esri ArcLessons web site has been quite popular for some years ago. They are not updated with the latest software technologies tutorials, but I find them very relevant particularly for the beginners. You will get understanding of various GIS concepts, not only how to use ArcMap.