LPI is a good start:
However, this is not so much of a course as a certification exam you would write after a period of self-study.
Redhat has some online and classroom courses, although I find them a bit pricey for my tastes:
Also, there are a number of Linux "bootcamps" available, which generally offer a super-concentrated classroom/lab environment with certification being the goal. Have a google for one in your area.
Also note that Linux Questions has a "certification" forum. If you read through old posts there it may give you more ideas.