Here's my take. I'm no expert so I'm sure I missed plenty, but I'm sure one of the boards many experts will be along to fill you in.
Mainspring housing (curved/straight)
triggers (short wwII type and longer modern type)
Combinations of different trigger lengths and mainspring housings can be used to tune grip size and trigger reach perfectly for your hand.
I like the ones with the bump. For some reason the just seem to offer me a better grip and deactivate easier. Its probably personal taste more than anything.
hammers (spur type/combat)
The spur type is a benefit if you like originality or if you like Condition 2 carry, since the spur makes for safer decocking and easier manual thumb cocking. The spur can bite some people with high grips or large hands, though. The loop style hammers won't bite you, but are difficult to manipulate with your thumb. Also race guns will have lightened loop style hammers for minimum possible lock time.
throated barrels and other minor internal things
Throated barrels help with feeding, especially hollow points. There are so many "minor internal things" that can be done to a 1911 you could start another thread on it.
full and original recoil spring guide rods
Some people say the full length guide rods make recoil smoother. I haven't noticed this. I prefer GI length because it allows you to rack your gun one-handed by pushing the slide against tables, fencposts, bootheels, etc. and it makes stripping easier.
ejection ports (standard vs. lowered and flared)
A bigger hole for the spent brass to come out of = more reliable ejection
Its not so much what kind of bushing you have, but how well its fit. The key to accuracy in an auto is the consistency with with the barrel returns to battery relative to the sights. In a 1911, a well-fit bushing is a big part of this.
Adds more grippiness. How grippy you want it and where you want it is all personal taste. Some people love or hate front cocking serrations, front strap checkering, etc. Its all up to you and what you want to do with your gun.
If you're left handed or very defense-minded and practice weak-handed in case of an injury, you might want an ambidexterous safety. If you want to be able to reach the safety easier or use it as a shelf for your thumb, you might want an extended safety. There's also a huge variety of widths of safeties to fit your personal tastes as well.