Sun's Courses free

well, not all are free,but there are several free and interesting, like this:

"topics about Application Server PE 9: ease of development for Java Platform Enterprise Edition (Java EE) 5, installation and basic administration, service oriented architecture (SOA) features, deployment, performance, developer experience, security, debugging and troubleshooting features."

These courses bring mp3 explanations, and they look very interesting...

more info:
SUN's course
Sun training

SwingLabs

SwingLabs is a Open Source Lab to explorer new ways to make easy application with improvements in performance and really pretty interfaces.

And they have a lot of components to download and use easily
for example:

Autentification window.

Typical WinXP's TaskPane
Important you need Java 1.5+
references: SwingLabs

Nautilus Scripts

An easy way to make a contribution to Open Source, is just giving more functionality to the existing tools and one of most easy is helping adding scripts or plugins to Nautilus, without necesity of change code absoluty nothing, just with scripts.

ie. a script that allows resizing images:
1 : Create script

#!/bin/bash
title="redimensionar_imagen"
scale="resize : <height>x<width>"

imgsize=
`gdialog --title "$title" --inputbox "$scale" 200 100 2>&1`

while [ $# -gt 0 ]; do
pic = $1
/usr/bin/convert -scale $imgsize "$pic" "$imgsize-$pic"
shift
done

2 : save this in ~/.gnome2/nautilus-scripts

3 : and ready, now it can use in nautilus


Download: pack with multiple scripts.

References : G-Script.