Take a look at the NIH Post-Bac Program. The experience is obviously lab/PI dependent but if you do your due diligence (talk to previous post-bacs from the lab, ask about what a PIs goals for their post-bacs ect) it can be a great experience. I've been in it for a year and a half (applying now) and its given me a chance to explore and meet faculty from NIH and extramural programs. Plus most people I know in the program walk out with a publication or two.