I bought
these ones from Amazon, which put out quite a lot of light. They're not for underwater use, but look great shining on the waterfalls and pond plants. These have an extra-long cord between the lights and the solar panel, so I'm able to put the panel in an area that gets a good few hours of direct sunlight.
I've got an older less powerful solar lights shining on the water lilies, and it looks really magical when it's all lit up.
In addition, I've got some underwater solar lights, which do give decent light. Unfortunately, they have a sort "nobbly" surface, which develops a biofilm rather quickly.