Bike helmet with a visor: I like more sunshade in addition to my sunglasses. I don't pay attention to helmets in the store that don't have a visor.
Lobster gloves: Best for winter cycling and if you get paranoid when you have Reynauld's syndrome in your hands, like I do.
Schwable Marathon Plus tires: Very sturdy, strong. Less prone to flats.
Cycling skort (or a running skort for shorter rides): Great especially if you bike in Europe, where you want to blend in a bit more with locals, rather than look overly-spandaxed.
Fun bike bell. Yea, I got me a little bell ringer: he's a construction guy wearing a brass helmet: ding-ding! I'm a kid all over again. Yea, I got this little guy, on my commuter bike.