At the Apple Event today, Apple announced a wealth of new bands for the Apple Watch, including an all-new "Solo Loop" band style. This band doesn't have any clasp or buckle, and is made out of one continuous piece of silicone.
To put it on and take it off, you'll just stretch it a little to get it over your hand, and it comes in twelve total size options for an "ultracomfortable" fit. To find your best fit, Apple provides a printable tool on its website.
The Solo Loop costs $49.00 and comes in Pink Citrus, Deep Navy, Cyprus Green, Ginger, (PRODUCT)RED, Black, and White.
A "Braided Solo Loop" comes in the same style but is constructed with a recycled yarn and available in five colors, running for $99.00. Colors include Atlantic Blue, Inverness Green, Pink Punch, (PRODUCT)RED, and Charcoal.
As a note, the Solo Loop and Braided Solo Loop are optimized for Apple Watch SE and Apple Watch Series 4 or newer. Sizes one through nine work with 40mm cases, and sizes four through 12 work with 44mm cases.
While these new bands should technically fit on the equivalent 38 and 42 mm casings from Series 3 and earlier, you may have to size up a bit to account for the slightly smaller casing if you want to use one of these bands with an older watch.