Spark plugs:  Champion plugs are good.  Normal spark plugs are fine. Platinium/ gold good for extra service, (thats it).  If you've got fuel injected STICK WITH Harley-Davidson plugs as if you don't it can bugger up the injection system as it alters the sensor reading.

Oil filter: When choosing another brand make sure it has a by-pass valve as promotes better oil circulation.  Synthetic media  is better than paper.

Battery:  if storing for months rig the battery up to an automatic charger every couple weeks. It will not go flat this way.  Check the terminals for corrosion every now and then,(esp. in humid places). A bit of Petroleum Jelly on the terminals protects from humidity corrosion.

Hope this helps somebody.

Shadow