I've done a lot of night rides, solo and groups, and by far the best to-be-seen lights are spoke/wheel mounted LEDs. Nothing else comes close. When I've been in a car at night watching for cyclists it's often easy to overlook cyclists passing broadside if they have only front and rear facing lights. But spinning wheel mounted LEDs pop out of the dark like nothing else, and are visible from any angle of view.
For awhile I used older style clip-on LED/reflectors that were pretty visible as well, but heavier than new style LEDs and could arguably unbalance the wheel slightly. Not a big deal on my commuter/errand bike though.
Otherwise, the Blackburn 2'Fer and Grid 2'Fer are excellent values and very versatile. They can be switched from white light for the front to red for rear, multiple modes, and can be mounted on the bike or helmet. I used one for years before losing it, and it retained almost full runtime per charge even after five years. Only weakness was the pocket clip -- it popped off my running shorts while I was jogging and I never found it again. But the provided mount held securely to my bike or helmet for years, even on gravel rides.
The Cygolite Dice HL-150 someone else suggested looks good too. I put that on my list.