As you might be aware, a number of countries have the Union Jack in their flag in whole or in part, a symbol of being part of the British Commonwealth at one time or another. Currently, this includes Anguilla, Australia, Bermuda, the British Virgin Islands, the Cayman Islands, the Cook Islands, Fiji, Montserrat, New Zealand, Turks and Caicos Islands, Tuvalu, and of course, the United Kingdom itself.
More countries used to include the Union Jack as well, but over time removed the Jack for a flag that is completely their own. This list includes Antigua and Barbuda, the Bahamas, Barbados, Belize, Botswana, Brunei, Canada, Cyprus, Dominica, Gambia, Guyana, Hong Kong, India, Jamaica, Kenya, Lesotho, Malawi, Malta, Mauritius, Myanmar, Palestine, Papua New Guinea, Samoa, Sierra Leone, Singapore, South Africa, Sri Lanka, St. Lucia, St. Vincent and the Grenadines, Sudan, Swaziland, Tanzania, Trinidad and Tobago, Uganda, the United States, Zambia and Zimbabwe.
New Zealand, though the likelihood is iffy, is being placed in the position to be the next country to make the switch. Prime minister John Key has expressed a desire for a referendum on changing the national flag; he prefers something more akin to what the All Blacks, the national rugby team, use: a silver fern on a black field, though he's open to something else if that's what ends up being wanted. But it's unclear as to whether it is. A recent poll showed 72% of the public being happy with the current flag and 28% in favor of a change, though whether that translates into what they'd do with an actual ballot in front of them is something of an unknown. In any case, with regular elections coming up, the original thought was to run the referendum alongside the elections, but with the numbers only at 28% in favor, that's been scrapped in favor of holding the referendum afterward.
There's also a secondary reason in play for postponing the vote: the flag has history behind it. People have saluted that flag, died for it. There's a day, ANZAC Day, observed on April 25 in both Australia and New Zealand, that serves as their bi-national equivalent of Veterans' Day. The first ANZAC Day was in 1915. The elections are scheduled for September 30. Nobody particularly feels like hauling down the current flag for the last time on the 100th anniversary of ANZAC Day, which might happen depending on when they decide on the new flag.
But, of course, that pales in comparison to the prospect of getting voted out of office over it.