I have to remember a lot of stuff. If you work with computers, you probably do too. Cory Doctorow popularized the concept of the "Outboard Brain" a long time ago, and it's still a valid concept. While Cory's approach was based around blogging, mine has used a simple program called nvALT for the last several years.
nvALT is a beautifully simple application that lets you write plain text notes about anything. Its main trick is letting you create or search for notes without having to manually manage creating or saving files; everything happens directly from the search bar at the top. If I need to take down contact information, I can just type "James Hobbs", hit enter, and immediately start typing phone numbers, company names, or any other relevant information.
Since all files are saved as plain text, they can easily be synced via your service of choice, and edited on any platform (right now, I'm using Editorial on iOS). By writing my notes using Markdown syntax, I can also instantly convert them to beautiful HTML or PDF documents using Marked. This gives me an incredible workflow that scales from one-liner code snippets to documentation for clients; all with no barrier to just start writing.