When I was at school, having paid close attention in Jake Stobbs’ Physics lessons, I realized that quite limited excitation if applied at the natural frequency of the bridge could get it to swing strongly and I demonstrated it.
Fifty years on, it was the highlight of my day to find that nothing had changed …

The Millennium Bridge, London opened and closed the same day because it was wobbling. But I bet at its worst, it did not wobble as much as the Dockwray Bridge.
Coming away from the Reading Beer festival, Brian Skeet and I discovered this new bridge. It is much stiffer than the Dockwray bridge but with a bit of effort, I was able to induce a noticeable swing.

I have found Nicolae Romanescu Park in Craiova, Romania which has what they call a "suspended bridge". I hope to visit it and check how much it swings.
And of course the ultimate in wobbly bridges is the Tacoma Narrows Bridge which opened in 1940 and wobbled itself to destruction in the same year.