Don't discount nebulae too with your Mak!
There's some technical tricks to keep in mind when using scopes that will help maximize what you can see. Aperture is one part, but how you use your eyepieces and exploit exit pupil is another part.
A 1mm exit pupil* is very easy to achieve with a Mak - it is a contrast sweet spot for our eyes, and will bring out details that can be otherwise impossible to make out at lower magnifications.
This last Sunday night at home in Sydney I was out with my 7" Intes Mak, also f/15 like your Mak, Darth. I was bowled over when I pointed the scope at the Swan Nebula with a 14mm eyepiece - cripes if I could make out the whole shape of the swan, body, neck and head, and further soft nebulous extensions out past its tail! So clear and easy to see! Yet when I dropped the magnification, the neck, neck and wispy extensions all next to disappeared.
So add M17 to your list of objects.
I was also able to make out the dark lanes in the Trifid Neb too with the same EP/scope combo, and impossible to spot the lanes at lower magnifications - don't forget, this is observing from under crap Sydney skies, not out bush. Things are much more challenging in the Big Smoke.
Globular clusters a plenty at this time of year. Many will resolve well, and others only partially, and still other resist resolution but will display different core intensities and expanse of halo.
M22, M28, M62 and M13 in Hercules are also ripe for the GC picking. But other less bright GC's are also good to chase as they all show different characteristics. A great challenge is to track down NGC 6453, a 10th mag GC that sits inside the boundary of M7. Sure it is faint, but it is a great test of optics, transparency and visual acuity. Knowing how to exploit your eyepieces is a great asset too. I also use this wee GC as a test piece for gauging the transparency of any given night.
DON'T forget galaxies! Remember how to exploit your eyepieces and exit pupil is the key to pulling detail, no matter what scope you have, Mak, Newt, frac, etc. Wavy noted a couple. Some others are M104 & M83 - heck, I've seen these in a 30mm finder scope from a dark site, and doable with a 50mm finder from Sydney. Some others include M84 & M77 (tricky).
AND there are also open cluster to boot! There's a trio of "treasure" OC's, the Jewel Box is one. The other two are the Gem Cluster (NGC 3293) and the Pearl Cluster (NGC 3766). M7, is not only BIG, but within its boundary also lie three other open cluster, half a doze tiny planetary nebulae, and of course that little GC. Another gorgeous cluster is NGC 6520 - this little cluster packs a tremendous surprise! It is small & intense, it sits smack bang inside the Cloud of Sagittarius, AND right beside it is the black-as-sin dark nebula The Ink Spot (Barnard 86). This makes for a very striking mix of textures and brilliance!
There's two other objects that should not be overlooked, though this time of year (winter here in Oz), they are not at their best - the Magellanic Clouds. There are literally hundreds of thousands of individual objects in both of these two galaxies. Open clusters, globular clusters, supernova remnants, emission nebulae, take your pick.
* To get a 1mm exit pupil is easy - the focal length of the necessary eyepiece equals the number of your scope's focal ratio! So, for an f/15 Mak, you will get a 1mm exit pupil with a 15mm eyepiece - a 14mm is near enough.
I hope this inspires you some more
Alex.