I've been working for a few years (I'm 25), but I'll be starting a phd in the fall and I'm going to leave my current job sometime in late spring/early summer. I'll be traveling and perhaps getting a job, but certainly not taking classes or doing extensive reading. Work sucks and the breaks like this one don't come often, so take advantage.
The last time I was in between jobs (Voluntarily, I might add. I didn't re-up my English teaching contract in Taiwan.) I took a month to travel overland via Phnom Penh-Siem Reap-Ko Chang-Bangkok, and then flew to China to do Beijing, the Yangtze, Xian, and Shanghia. Best. Decision. Ever. I should mention that I met some other grad students along the way who just couldn't force themselves to do summer work, so consider this idea.