For some inverts suggestions (all but one of these should be 1" or less max):
-Dwarf Hermit Crabs (Dwarf Red Tips, Dwarf Blue Legs, Dwarf Yellow Tips, Hidden Hermits, Dwarf Zebras, etc.)
-Acropora Crabs (Trapezia spp.)
-Porcelain Crabs (typically Petrolisthes or Neopetrolisthes spp.)
-Pom Pom Crabs
-Micro Brittle Starfish
-Aquilonastra Starfish (these are known in the hobby as Asterina Starfish, and often considered pests because they reproduce so readily and frequently in our tanks).
-Rusalty's (Aquaculture Nursery Farm's) Green Lantern Shrimp
-Bumblebee Shrimp (as a note for these guys, from all verifiable accounts, while they do inspect starfish and seem to feed off of something on the starfish, they don't seem to actually do any damage to the starfish, and they don't seem to actually eat them at all)
-Sexy Shrimp (these guys technically get up to 1 1/2")
-Chitons
-Shellback Crabs (Hypoconcha spp.)
-Skeleton Shrimp (Caprella spp.)
All kinds of "pods" (Copepods, Amphipods, Isopods, etc.) would work. Plenty of snails would work, as would some limpets if you can find them. If you're willing to feed phytoplankton regularly, then you could keep some bivalves (clams, oysters, scallops, etc.), barnacles, and or feather duster worms too, several of which would be small enough to meet the criteria.
I'm sure I've missed some suggestions, but this should be a decent start for you at least.