Some months ago we had a CI server shootout, mainly between Atlassian Bamboo and Hudson. We allowed two months for carefully evaluating both of them. And in the end, Hudson was the close winner. One feature though, that we liked a lot about Bamboo, was the tight integration into Jira (surprise, surprise). With these new portlets for Jira, Hudson can measure up easily: job overview, recent builds and charts of various now can relatively easily be integrated into the Jira Dashboard.
Download and installation instruction: jira-hudson-plugin 1.0
Ah, by the way, this is published under the Apache 2.0 license. At some point, this will probably move to the Atlassian plugin exchange. Please comment if you find this useful, and what other features you would like to see.
Update (2009-09-10): The plugin is now listed on the Atlassian Plugin Exchange.