Ever tried stirrupless work? You probably have, but just a suggestion. I used to get really scared, now I love it. If your horse can't jump, then I couldnt suggest anything else. But, if you have a friend/someone you know with a jumping horse, I would suggest chase-me-charlie, you have to set up a row of jumps, and each round you have to increase the hight, good to play in pairs, or to see your standards :)
I put a halter on my horse and let him walk around and eat, if you really trust him you can just use a halter to get on bareback and then take it off and let him eat and maybe get him to walk and trot around wiht him buds, if he has some in the pasture.
We do the obstacles too as mentioned a few responses back. It's fun to practice and fun to come up with new ideas. We have the boardwalk idea, carwash, tires set up like military courses do when they run solders through, yard spinners to go past, tarps to get creative with... More ideas we don't have set up yet is a teeter totter, water feature of some type, I've seen pool noodles used in some creative ways.
I'm a big trail rider, so the obstacles just help my horse be so much more level headed out on the trail. :)
You know what else is a blast with a group of others? A treasure hunt on horseback.
I got to go on my first CMO ride this year (Competitive Mounted Orienteering) and I am totally hooked now. It's a national organized ride, but we've talked about setting up mini courses here at home for the fun of it too.