Landing in Cleveland for that big conference and discovering that you left your toiletries bag at home is inconvenient. Finding that you left your cell phone charger right next to it is catastrophic. PackWhiz is an online packing list generator that helps you avoid those kinds of unfortunate surprises.
Building a packing list in PackWhiz is hardly rocket science. The site leverages your Google account to log in, and you can either build a list from scratch, or check some preferences to let the site create one for you automatically. Either way, you can arrange your list into categories, add and delete items, rename them, and add comments to your heart's content.
When you're done crafting a list, you can keep it private or publish it to a public URL, where you can share it with your travel companions. There's no limit to the number of packing lists you can create, and the service is free.
While PackWhiz is kinda cool, it's obviously not the only site out there offering this kind of service. I've also used Don't Forget Your Toothbrush. And the simplest example of online checklists I've ever seen is the does-exactly-what-it-claims-and--not-a-single-thing-more Printable Checklist.