You want one with a good standardization of Boswellic acids.
As mentioned above SNS Joint XT does contain a good extract and another comprehensive product with a solid Boswellia dose would be Controlled Labs Health IQ.
If just looking for Boswellia in isolation be sure to check the standardization. Swanson offers a solid single extract product (contains 5-loxin) and Life Extension offers another (apresflex).