You'll probably have to try a few until you find one or more that gets their attention
Dehydrated liver treats, hotdogs (cut into small pieces and cooked slightly in the microwave so they're not slimy), cheese, meat (chicken is the favourite in my house).
For treats you can buy, Wellness Wellbites are the highest value in my house. Large pieces but easily torn into smaller, my dogs will literally drool when I'm using them for training. Zukes is another good company but they just got bought out by Purina/Nestle so I'm no longer using them personally. Rollover is another treat, it's a large hunk which you can cut into smaller pieces
When I'm training I use a treat bag with a multiple types in it so the dog never knows what I'm offering next, I've found it's eliminated any expectations for the dogs
Jasmine - Female Miniature Poodle - born Aug 15, 2010
Loker Delgado Von Stalworth - Male GSD - born Jan 26, 2012
Koda & Zazu - 5 year old male cats
Alex - Male Cocker Spaniel (rescue) - RIP Cuddlebug 2007-2010