Bluegill, definately not, They can get over a foot and they're MEAN.
Just my opinion, but I think your best bet would be a few pumpkinseed and a few green sunfish. Pumpkinseed are more colorful than the others anyway. Green sunfish are very basslike, plus they look really nice when they're adults. These are both fish that don't get massive like a bluegill and will likely max out at 8 inch at the MOST.
Make sure to put driftwood and either some fake plants (or live, though more sensitive plants may be uprooted or destroyed. I had like with valisnaria.)
I'm not sure if you have longear up there, but they seem to be more docile than the rest. If you can find them they'd probably be a better option than pumpkinseed.
I would keep less pumpkinseed than greens. IME greens will chase and posture but they aren't as purely aggressive as pumpkinseed.
Green sunfish may not look terribly interesting as juveniles, but they will grow into a very basslike fish.
I wouldn't keep more than six or seven of any of these fish in a 55g as adults.
Here's my green as a juvenile, about 2 1/2 inches long (Click for bigger):
Here's mine now:
Check out that mouth,
