Bitcoin USB miners
The first Bitcoin USB miners were the Sapphire Block Erupters. They have 330 MH/s of hash power which will give you less than $0.01 per month. This is the best choice if you want to see how mining works, but just the like with most USB miners, a profit should be least expected.
GekkoScience Compac USB Stick Bitcoin Miner
Just slightly better than the original block erupters is the GekkoScience miners. It will yield you about $0.15 per month, which will give you more than a dollar in 12 months! The device runs completely silent, as the company claims. It works with just one USB port.
Bitmain Antrouter R1 Wifi Solo Bitcoin Miner
Although not exactly a USB miner, the Bitmain AntRouter is just similar. It's cheaper, but with that you just get a 5.5 GH/s, a low one which is a little over $1 per year.
What’s great in this is you can do some mining while providing internet for all your devices because it works as a wireless router.