Hairy Woodpecker, courtesy of 1Watt Hermit
The larger of two look alikes, the Hairy Woodpecker is a small but powerful bird that forages along trunks and main branches of large trees. It wields a much longer bill than the Downy Woodpecker's almost thornlike bill. Hairy Woodpeckers have a somewhat soldierly look, with their erect, straight-backed posture on tree trunks and their cleanly striped heads. Look for them at backyard suet or sunflower feeders, and listen for them whinnying from woodlots, parks, and forests.
Cool fact: Hairy Woodpeckers find their food by feeling the vibrations made by insects moving about in the wood. They also can hear the insects munch on the wood!
1Watt Hermit has a delightful Flickr site with many shots of the birds he watches through his window. I chose one but recommend them all, and recommend you try watching some in your own yard too.