In my research I've found these two, which are only explaining the basics.
http://workshops.opengeo.org/geoext/index.html
ftp://ftp.itc.nl/pub/jmmgnl/GeoExt_Workshop/GeoExt-Workshop.pdf
And of course the native (but short) tutorials and examples on the GeoExt website.
Can anyone know about other resources?
Thank you!