For experienced testing practitioners I would recommend the four-day ‘Certified Agile Tester’ (CAT) from iSQI®. There are however other shorter agile testing qualifications available offering Foundation Level style exercises and exams.
The iSQI® Certified Agile Tester qualification can be seen as a 'Gold Standard' for the current software testing qualifications offered by ISTQB® at Foundation and Advanced levels and by iSQI.
This article focuses initially on agile qualifications, but the points made about the learning objectives, examination methods and practical aspects of the courses also apply more generally to Foundation and Advanced levels of qualification.
ISTQB®, iSQI® and TMMi® certification schemes examine software testing knowledge and skills via clearly defined learning objectives set out in their syllabi.
Whilst I agree with some of the points made at http://www.professionaltestersmanifesto.org/, I disagree with the final clause about certification in the opening statement (my italics):
“… standards compliance is no substitute for knowledge and skills, and that possessing a certificate demonstrates neither."