Via the Wikipedia aggregated poll chart, New Zealand opinon polls for the year 2011.
Update: A caveat from the creator of the chart:
As the person that created that graph, may I remind you all that there are three types of lies: lies, damned lies, and statistics.
This is not the current version on wikipedia, but someone challenged (perhaps validly) on the talk page, whether there was some very recent movement not evident on the main graph. I changed the parameter on the smoothing line to make it more sensitive to recent changes. With the sensitivity to recent polls increased, it does seem like there has been some quite strong movement in the past weeks, but interesting, I tested an intermediate value that would give rise to a different interpretation (mainly that Labour’s support is stable, and slower change for National and Greens). So exactly how you interpret the poll trends hinges on the value of the smoothing function, but if you buy into the more sensitive version, then there does seem to be something of a swing in progress.