I am seriously considering going for a graduate certificate in GIS. I would think that working your way through a few Master's level courses would be good way to learn GIS, in more depth than just knowing what buttons to push on the software (and get something to add to the resume). Of course it is more expensive, but you could take just the first course (intro to GIS) and then drop out. I've found a number of programs that look good, and I'm even working up a grant proposal to fund folks at my utility to take these courses (we're moving heavily into GIS for our system and asset management). Here's a list I put together recently. The Penn State program looks like a winner:
Johns Hopkins: 5 courses ~$17,000
http://advanced.jhu.edu/academics/certificate-programs/geographic-information-systems/
Penn State - 4 classes. ~$8,500
http://www.worldcampus.psu.edu/degrees-and-certificates/geographic-information-systems-gis-certificate/overview
USC - 4 courses ~ $27,000 (yikes!)
http://gis.usc.edu/
Northeastern - 6 classes, around $10,500:
http://www.cps.neu.edu/degree-programs/graduate/graduate-certificates/certificate-in-geographic-information-systems.php
University of Denver: 6 courses, ~$13,000
http://universitycollege.du.edu/gis/degree/certificate/geographic-information-systems-online/degreeid/31#overview
University of West Florida - offers both undergrad ($6,000) and grad GIS certification programs ($8,700)
http://uwf.edu/gisonline/CourseOptions/GISCertificate.cfm