Replaced my valve cover gasket about a year ago, but it's started leaking again (probably because I didn't follow the proper bolt tightening procedure...). I'm planning on doing it over again and was wondering what other items could be serviced as well while I have all those parts off the engine.

 

Maybe the oil filter housing seal if its leaking, though most of that is from underneath. Inspect all the vacuum lines while you have it all open. Inspect the thermostat housing seal, plugs wires if need be and coil. All I can think of.