1. Sugary substances
Chocolate in any form is always appreciated, but on cold, miserable winter days a nice warming hot chocolate or Milo (link for those not in Milo-drinking countries) can make it all seem a little better.
2. Cute things on the internet
It's an internet cliche because it works - my girlfriend (who now has a blog!) is usually my main source of such links. However, I always keep this one on standby for particularly bad days - it takes a cold soul indeed not to find this one cute:
When it's hard for me to concentrate on things I should be actually working on, I sometimes find doing some puzzles a good way to keep my brain ticking over. My current favourite is Project Euler (warning - non-programmers will really struggle!)
I'm regularly surprised by how much music can help turn a mood around or focus the energies - I've never been much of an electronica fan, but iriXx's work has given me some of my most productive afternoons. I tend to listen to the same music over and over again before moving on to another artist - one on my current high-rotation list is Tasmanian act Enola Fall.
Sometimes it's good just to blow off some steam - as screaming in my office would probably cause some distress in my nearby colleagues, writing things down is a little safer. Chatting to friends online, writing blog posts, writing out to-do lists and plans - it all helps!