Question: 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  *Lutz Roeder .NET Reflector*  - for Java

Answer: 
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?](https://stackoverflow.com/questions/275120/java-how-do-i-know-which-jar-file-to-use-given-a-class-name "Java: How do I know which jar file to use given a class name?")
`java -xf some-j.jar` will unzip a JAR file.