Daytime flashing front lights
Being seen is being safe, and that's every bit as important in the daytime as at night. You've probably noticed many cyclists running with flashing headlights during the day, and often flashing tail lights as well. There is no question this improves the likelihood of someone seeing you! And with the newer, inexpensive, lightweight and rechargeable lights available, why not?
Keep in mind that, when fairly close to a car, visibility isn't the issue, but rather whether they're paying attention. When driving, people "zone out" from time to time. Who hasn't at some point been driving along and realized they don't remember anything about the last 10 or 15 seconds? The goal of a daytime flashing light is to be visible for a long-enough period of time (from far away) to catch the driver's attention, because, once they're paying attention, they're not likely to forget about you as you get closer.
The lights shown below are the best of the best. These are the front & tail lights the staff of Chain Reaction actually uses, night & day.
For daytime front use, the Serfas Thunderbolt is the best in terms of side visibility (viewing angle), and its strap-on design allows it to be placed just about anywhere. Its downside is the short time between recharging; about 1.5 on high flashing mode, and 7.5 hours on normal. The Lightning Bug 150 isn't as visible from the sides, but, in flashing mode, lasts much longer and doubles as a useable light for seeing where you're going at night. If you need to see where you're going at night, the Bontrager Ion 700 can't be beat. Small package, great beam pattern with an amazing amount of light. It can also be used as a daytime flasher as well.
Do less-expensive options exist? Yes, many. But they lack the versatility, function and durability of the two I've listed here. These are awesome moderately-priced daytime lighting solutions that recharge off the USB port from your computer or iPhone charger. The $10-$30 options don't come close to what these offer.