Christin:
You can also check out the
Marketo Launchpoint site. There are agency-managed services from Marketo partners listed there. In terms of designs and resulting products for the handoff, just make sure you have a result that a team can deal with. Some designs are downright difficult to replicate and then change/update in Marketo's editor itself. Responsive Marketo landing pages can be difficult to create/maintain as well, since the WYSIWYG editor isn't quite designed for it.
Best,
Edward UnthankMarketing Operations Specialist
Yesler