The Crosman 2100 and Daisy 880 are two pretty common BB/pellet guns sold at Walmart. They're both a great way to learn to shoot for cheap, or to take out some tasty small game at close ranges (anyone who tells you it can't be done humanely hasn't tried it, or has a "real" gun bias). Both guns have their selling points. I'm hoping that somewhere a young person or a new shooter will read this and make an informed BB gun purchase.
Daisy 880
Pros: $45, included scope, very light, accurate with BBs
Cons: cheaply made, sights glare badly in sunlight
If you're purchasing the air rifle for target practice or for a child the Daisy 880 is the better bet. Both airguns are BB repeaters and single shot pellet. For those who don't know what this means you have to load one pellet at a time, where with BBs one only has to pull the bolt back.
Crosman 2100
Pros: $55, very accurate with pellets, built sturdy like a powder firearm
Cons: horribly inaccurate with BBs
The Crosman 2100 is an awesome small game gun. Load a pellet, pump it up, and head into the tree field in pursuit of critters. Unfortunately the 2100 isn't much fun at all at the gun club. Loading one pellet at a time gets old, and the 2100 can't consistently drop a can at 25 yards with BBs.
I'm proud to say that I own both rifles. The Crosman is for those rare hunting expeditions and the Daisy is what I take to the gun club when I can't afford to be shooting a brick of 22lr.