A good place to look for arguments on which you can practice your argument mapping skills is at TruthMapping. Not only does it have a database of arguments that have already been open to challenge and debate, it also has a primitive map of each these arguments, which may help you get started
As an example, I picked an argument from TruthMapping about whether or not determinism can be shown to be either true or false:
1) PREMISE: The only claims about public reality which can be considered true or false are those which can in principle be submitted for experimental evaluation.
2) PREMISE:
Determinism claims that all events in the universe are controlled by physical laws.
3) PREMISE:
No matter what the outcome of any experiment, a determinist can claim that it was determined.
4) FROM 1,2 AND 3 IT FOLLOWS THAT:
There is no experiment which can prove the truth of determinism.
5) FROM 4 IT FOLLOWS THAT:
Determinism can be neither true nor false.
The primitive argument diagram looked like this (I have dropped statement 6 from the written statements, since it was a step further than the thesis of the argument)

So, having played about with it, what did I come up with?

You will probably see, that in addition to the objections being placed within the diagram itself, the structure has also changed. This is a great advantage of using argument mapping, because when you see the arguments laid out in diagrammatic form, you also notice that what you originally thought was a supporting claim actually requires a suppressed premise, or what you assumed were separate premises are in fact mutually dependant.
You can download the Rationale file Download Determinism.rtnl. I have included a bonus argument on determinism (a picture of its structure follows) - but it has not been analysed. I leave that as an exercise for the reader.
