Can you get some exercise today? It completely changes my mood for the day if I get in at least 30 minutes of moderate exercise every day.
I prefer a strenuous uphill nature walk, but there are so many things that are enjoyable depending on your interests. Dog-walking? Running? Stair climb all the steps you can find? Dance - I have Zumba DVDs and love them. You can find exercise video on YouTube, or rent them from your local library. Just get out - exercise is a huge mood enhancer.