I say "the birdfeeder is the best cat toy evah!" but I spend most of my weekend mornings watching the action myself (as I type this, the cats are asleep well away from the backyard windows, harrumph).
The feeders are squirrel-proofed, but I accidentally bought a seed mix with peanuts and the birds here don't eat them, so I've been scattering the peanuts in the snow when I refill the cardinal feeder (next batch of seeds is only black oil sunflower, millet, and cracked corn). They've been crawling under the store, and jumping from bootprint to bootprint, and when one finds a motherlode, he'll chase the other squirrels away...but while A is chasing B, C will move in and start digging around. Hours of entertainment you can't buy in stores.
I haven't been keeping good track of which birds I've been seeing, but off-hand: three different kinds of finches, juncos in the winter, titmice, woodpeckers, blue jays, and of course cardinals.
Also have a few starlings, who will move in and empty the suet feeder in an hour. Attention people from NYC who get all butthurt that the hix from the stix don't all admire you 24/7: Start with the fucking starlings.