In the world of AWS acronyms abound. The term ISV gets thrown around a lot but it's relatively easy to unpack. First, ISV stands for Independent Software Vendor. What this means is a company who product or service is build in AWS Cloud, but is not an AWS product.
Digging a little deeper, there are two types of AWS partners: 1) Consulting Partners and 2) Technical Partners. Consulting Partners provide professional services (consulting, custom application builds, system integration, managed services), while Technical Partners - also known as ISVs - provide their services on a subscription or a pay-as-you-go basis.
You can find a list of all AWS Partners, technical or otherwise, on the AWS Partner Finder:
Once you've completed your initial search (say with the location "Los Angeles"), you can then select only for AWS ISVs by checking the "APN Technology Partner" checkbox on the left hand side: