Well, a "miner" can be a CPU, GPU, FPGA, or ASIC which I have placed in order from the "slowest" to "fastest." Here is a great list of miners one can acquire to use for mining: https://en.bitcoin.it/wiki/Mining_hardware_comparison.
It really all depends on what you want to mine. BTC which is the most common but because of its high difficulty can really only be mine on ASIC miners. This is true for all SHA-256 based digital currencies. The problem is the cost of an ASIC miner can run you from a few hundred dollars to a few thousand dollars. Not cheap and we are talking about needing a "few" of these rigs to be cost effective which a lot of people join pools.
Now if you are looking to make a profit and do have some money I recommend mining scrypt currencies like Litecoin, Dogecoin, or Vertcoin which have a low difficulty and if you can get 1 or 2 decent scrypt ASIC miners you can start making a decent profit quickly and pay back your miner in about a month.
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