Web/Cloud-based applications are currently a hot topic, but I have to recognize that though I see in it an enormous potential, my daily used is confined to a very narrow selection of them:

• Evernote: My number one application where I throw ideas, notes, screenshots...etc
• Doris: I have used Toodledo and Remember the milk, but both application miss the only one feature I really need and that Doris has got, it is the possibility to reorder the tasks by a drag and drop. Don't expect an advanced type of application, but what Doris does it does it good.
• Google docs: If you couple web file storage to a performant on-line office suite, you get Google docs.
• Google reader: This is where I centralize and manage my RSS feed list and that I query using Newsrack on my iPod Touch
• Amazon S3: The best value for money for file storage. It is not only reliable, but it is also an industry-grade hosting for a price that is ridiculousIy low. use it through the Jungle disk software which I have luckily purchased at the time it still had lifetime licenses.

Yes, I know, you may think there is much more on the web than the five applications listed above, but believe me I have tested much more than these but let's face it, more is an overkill and most of them will end up as dead links in your bookmark list. These sites are the essential web based application set you should consider.