Depending on the scope of the company you can try to offer a broad variety of services with your co-marketing campaign.
For instance, just to name a few:
- any services related to SEO optimization. SEO and UX are strictly interconnected; most of the clients who are looking for UX reviews may be interested in SEO audits as well
- any services related to designing ( graphic designing, logo building, naming, etc) are also strictly connected with UX. Additionally, you can gain the halo effect of being endorsed from an UX design company: this helps in terms of reputation
- any more technical (back end) services related to content management systems
- and, broadly, any digital consultancy services.
This is just a short list since the options are countless: I work for a global brand and we have run several co-marketing campaigns. It's key understanding the partner you are engaging with to define the best way of planning the campaign.
Happy to chat for more details.