Insulin, GH, IGF, B12, HCG. That's basically it for bbing drugs in general. You can do PK's that way as well, or benzo's, but that's not the kind of thing anyone here would do of course
B12 is either one bro, I've never done it IM and it works quite well sub-q. Actually, every one of those listed will work both ways, but medically they are easier to do sub-q b/c of injection frequency.
Sub-q is actually done in the fat most of the time. A TB skin test is actually more shallow than sub-q, it's a skin-pop. Meds done sub-q like GH, slin, etc, are typically done in the fat of the abs most often, just pinch and poke.
If it is in the fat it IS still sub-q however the vascularity of adipose tissue is poor and absorption is slowed. It is preferable to inject either below the dermis and above the fat or below the fat itself. For lean individuals it is preferable to pinch the skin and inject at a 45 degree angle. Sites for injection include the anteroir abdomen away from the belly button and anterior thighs if you are injecting yourself. If someone else is doing it you can also utilize the posterior upper arm and the area over the scapula. The reason for these sites is the low presence of blood vessels and free nerve endings. Hope this helps.