Once you have a large number of projects in JIRA creating an issue can become a bit tedious, scrolling through the long list of projects to choose just the right one. JIRA (Enterprise edition) already provides Project Categories that you can group projects into, so without further ado, here's a JSP hack to reduce the size of that list of projects by letting you select a project category first.
The modified file for JIRA 3.13 is createissue-start.jsp and replaces the file of the same name in your JIRA instance. There should be no need to restart JIRA. The usual disclaimers apply, drink responsibly, don't drive and derive etc.