I have always used DJ Java Decompiler to solve Java Applets, but my 'trial period' has now expired. Does anyone have any other good programmes that can view .class source, or is able to provide me with a key?

This site can show you plenty....

Maybe try an older version of DJ.
iirc 3.9.x is without the trial period, else try 3.7.x
I think older versions are still around and are quite equal to the latest.
You can even replace the jdec.exe with a more current version

Greetings
Towley

I believe so too, though i use 3.7

You should give a try:

http://www.kpdus.com/jad.html

I think jad is the most used decompiler (i meant jad instead of jdec above)
Many decompilers make use of it.
Also DJ is using jad to decompile stuff, its just some gui for it.

I also use mDeJava. I have a couple installed