I use the Evernote web site, Mac application and iPhone app to capture information from the web, from images, from PDFs and assorted notes. The apps sync to the Evernote site and any image or PDF is OCRed so I can search on any text in them. I use multiple tags on each record so, combined with the ability to search any text contained in the item, I can easily locate anything in my data store. A day-to-day example is, I take a picture of any prescription label I get with my phone and send it to Evernote. Then, I can easily find it wherever I am when I need a refill. I also scan in receipts and then destroy the originals to cut down on the pile of paper that used to obscure my desk.
I keep track of to-do lists with Remember the Milk. I've never liked the name but it's the best task manager I've used. I can set up multiple folders for GTD-type use and it also has an iPhone app. I can create, maintain and complete apps on the phone and it pushes a notification each morning with the tasks that are due that day.
Not affiliated with either company, just a satisfied user.