I 'd argue taking time off will definitely not hurt you. Putting some years between you and your not-so-hot undergraduate record will be a good thing; you can speak to the growth in your maturity while you're away. If you do the peace corps or something similar though, you should really try to take some graduate-level courses in the meantime, maybe through a correspondence program or something, just to show you have the capability to persevere through graduate level coursework. If you do the masters, get some papers out, and definitely go the thesis route to graduation. You need to do better than the expectation to make the MS route an effective counterpoint to your undergraduate record--think 4.0 or close to it, and a first authorship.*
You will in general have a very hard time pushing back into the field. It's very competitive, so a questionable history can be a real killer. Not impossible though, and the longer you work at it the more likely someone will be to take a chance on you.
*if you do decently well (upper half) in your masters program with good recommendations, you'll probably get in somewhere. But if you want some choices, go for excelling. Bad GPA's are a real grad school killer.