Here are few suggestions, which you can bring together or one-by-one.
Bring awarding best team member of the sprint in your Retro:
- Ask the team to vote during Retro
- Collect vote in room by raising hands
- Use vote box to vote for best developer / tester of the Sprint
- Before Retro, run a survey to collect
- Instead of asking for a single rating from each team-member, go with ranking approach. Ask team to rank for everyone's choices as 1.2.3 and mark them with values 5, 3, 1 respectively. Use sum of values of all team members to determine The Developer of the Sprint.
Things that were identified in previous Retros (whether practices or procedures), try to gauge their improvement paths - Identify maturity level on a scale of 5 and make team to discuss it.
- This helps to know what they discussed earlier (as a refresher), as well as if they are sticking to it.
Identify wastes in the previous Sprint - This helps to understand why something is not necessary and make the Team to qualify it.
Discuss Customer Satisfaction Index/Factor from previous deliverables.
Bring innovation - Any change to an existing approach - Determine if there any new way of trying to do something, and implement them - Brainstorm.
Every 3-4 Sprints, show a 5 minute demo of the product before the 3-4 Sprints' and show the current one. (Maybe record a video of the product every Sprint-end). This actually gives great motivation to the Team as, with the speed in which things are delivered, people get less time to look at the path traveled.