I always put a tbsp. or so of ground flax to add some extra nutrition benefits. I use dried fruits a lot in my oatmeal, especially chopped dates. I use chocolate malt flavored Ovaltine as well, although i'm now looking for a vegan version of something similar. Chocolate makes it creamy and just plain yummy!
I also have started adding strawberry preserves as well. You can also try other spices, such as pumpkin pie spice, which is a blend of spices like cinnamon and nutmeg. There's also vanilla extract (or any extract flavor really!), any fresh fruit, maple syrup, any of the nut butters, various nuts, any of the dairy free milk substitutes (especially the flavored ones!). I am always experimenting with my oatmeal so I don't get bored.