I reckon you're lucky to get The Crucible - its a fantastic text with alot of depth and you can draw upon many things to make your analysis even more sophisticated and to impress the markers.
For example - you should look at, or even throw in things relating to Arthur Miller's message concerning McCarthyism and the Communist hysteria at the time. You can also look at Arthur Miller's Theatre Essays and what he says about the tragedy of the common man (linking that to Belonging - particularly with Hale or Proctor).
Therefore for related texts it might be interesting to look at other works that also explore cold war tensions - possibly from a communist perspective.
You may also choose related tests dealing with the Puritan era and all the restrictions of the time. Some possible authors are Nathaniel Hawthorne (The Scarlet Letter) whose exporation of puritan culture and Hester Prynne's liberation in rebellion (ie. breaking away from belonging and conformity) has very interesting parallels with The Crucible.
You may choose to look at the human vs. nature, frontier aspect of The Crucible, and a good text for that is the american transcendentialist writer Thoreau with Walden (about man's retreat away from community to join with nature) - interesting contrast with the Puritan view of indians and Massachusets in The Crucible.
In choosing a related text, I suggest you find AREAS of analysis in your core text that you wish to explore, and then find related texts who overlap in those areas - that way you have a clear link, and your analysis tends to become clearer and it enables you to have a better thought out thesis.
Related texts that work well are texts which you can use to directly compare or contrast. They are very much looked upon favourably if you can find conceptual, historical or social links as well (though not necessary). Main thing about using related texts effectively is that you demonstrate a RELATIONSHIP - ie. how your related text extends upon, enriches or sheds new light upon your core text.
FYI I also did The Crucible, and my related texts were The Scarlet Letter and The Lieutenant (Didn't end up using it - due to the question stipulating ONE related text in 2009), and as well I quoted from Miller's Theatre Essays (and his theory of tragedy) to support my analyses.