Recently we at JBoss® received licenses for JIRAClient. It is a cool desktop app (written in Java) that serves as a frontent to Atlassians JIRA bugtracking sytem. One of the nicest features here is offline mode: JIRAClient is ablw to download issues to its local database, so you can work offline and upload changes later on.
The staff at Almworks is very responsive in the forums and also open to suggestions.
If you are using JIRA on an daily basis, then you should definitively check out JIRAClient.