I have recently started using two tools that probably everyone but me knows about, but just in case!
Simplenote. Straightforward text files that you can access and update in your web browser or through various clients, that sync automatically. For instance, I have a pinned "to do" note that I keep open throughout the day and jot down anything that comes to mind (shopping list, stuff to do at home, etc.); "hobbit reviews I am not reading yet"; the most recent book added to the NYPL's ebooks site, so I know if anything new has been added; boilerplate HTML for the Tor.com Hobbit posts; and so forth. There are lots of clients; I'm using ResophNotes with no complaint at home.
Yes, it's true that this means I'm using three different web-based services to organize my life: Simplenote; Remember the Milk for recurring or future-dated tasks; and Google Calendar for appointments. [*] This seems inelegant, and yet they all do what I need them to do—which includes setting recurring tasks, sharing appointments with Chad, and being available in a browser (as I neither have nor want a smartphone), so hey.
[*] I have the last two open all the time in GMail, using the RtM for GMail gadget, the Google Calendar GMail Labs gadget, and a CSS trick to give them more room (in Opera I can do this with a user stylesheet and no add-on).
Evernote. This is kind of the philosophical opposite from Simplenote, and is designed to store and tag basically everything. I use it for a very specific purpose, which is to keep fanfic: my prior find-it-later system was too much work and never got done, but now I use Evernote's bookmarklet on a fic's web page (the HTML download page on AO3 is good for this, but you can also highlight just the text on an LJ/DW journal entry), and then it's saved to my various computers and can be tagged and full-text searched within Evernote. I can also occasionally export from it to put on my ereader, though if I get a tablet (as I'm contemplating), I can use their Premium feature for offline data availability.
What are your go-to online services to make your daily life less chaotic?