I live in the Pacific Northwest, Canada's "Wet coast" (Vancouver), and we get a lot of rain here. Misting rain, drizzle, showers, downpours, monsoons, you name it. Rain central. Anyway, I commute daily, about 5 miles each way, regardless of weather and I have found the following articles of clothing very helpful for dealing with rain:
Rainlegs! Great for keeping the most weather exposed part of my legs, thigh-tops & knees, dry.
I like to combine them with a pair of waterproof shoe covers like these at REI: Shoe-covers!
Those two articles combined with a light, water-resistant and well vented jacket (with a tail) will keep me dry and comfortable for up to thirty minutes in an absolute downpour. The water resistant jacket doesn't have taped seams, uses DWR and will generally begin to give up the ghost around the seams after twenty minutes of heavy rain. For heavy rain I wear a waterproof cycling jacket. Not as breathable as the water-resistant and definitely not as well vented either. In order to avoid creating my own personal & portable sauna wardrobe choices have to be well thought out.

The Rainlegs and shoe covers are great for keeping the rain out. If it's really nasty out with water flying at me from every direction the unprotected spaces, shins, backside, can get wet. I have full on rain pants but don't find them particularly comfortable to ride in and generally only use them for longer rides in (cooler) monsoon-like conditions.

I don't bother with a helmet cover. Gloves, usually some water-resistant cool weather gloves. Water-proof "lobster-claw" glove covers should things get really wet.

And fenders. Full fenders.