Blogger kortina describes how to set up gcalcli—Google Calendar's command line interface—on the Mac for quick access from the Terminal. You'll need to install Python along with gcalcli and an alias.
With all this stuff set up, creating a reminder for myself is super easy: I just hit Cmd+Shift+i to open iTerm (see Setup Global Keyboard Shortcuts to Open Any App with Quicksilver), then type q '9pm write blog post about gcal' and I have captured the thought and can get it out of my mind and focus on whatever task is at hand.
Of course, if you're already running Quicksilver you can just use the GCal Quick Add plugin. Since we last mentioned gcalcli, it's been updated to include a remind-link monthly calendar layout. Here, have a screenshot.