<p>What would be the easiest way to view classes, methods, properties, etc. inside a jar file?
I'm looking for something equivalent to the very useful <I> Lutz Roeder .NET Reflector </I> - for Java</p>

I usually open them with 7-Zip... It allows at least to see packages and classes and resources.
Should I need to see methods or fields, I would use Jad but of course, it is better to rely on (good) JavaDoc...
Now, somewhere on SO was mentioned some Eclipse plug-ins, to find in which jar file a class is located, perhaps they can do more (ie. what you requested).
[EDIT] Reference to SO thread. Not what is asked, but somehow related, thus useful:
Java: How do I know which jar file to use given a class name?