TextExpander is one of those small pieces of software I use every single day and can't imaging doing without. The premise is simple, a short bit of text expands and turns into a large amount of text. For example, I use dates a lot in my day job, so I have several simple snippets that dump dates in the right format. Number one on the list is ,ds which expands into 2014-03-22.
MacSparky's package of Date Time snippets has some great examples of date math, and emphasizes the power of TextExpander. He added some delightful snippets to find future dates or ranges. For example, xdnm returns the date for next Monday. The snippet runs a bit of AppleScript code, determines the correct date and returns, 2014-03-24.
I wont include the code since it isn't mine, but I highly recommend checking out TextExpander. It will save you time in many small ways.