Bitcoin - by Investopedia
How Bitcoin and Bitcoin mining works

CoinMarketCap
List of all popular coins, sorted by market capitalization

WhatToMine
Calculate the mining income based on your mining hardware. For GPU, CPU and ASIC mining. Lists popular coin for mining.

ASIC Miner Value
Great resource for shopping ASIC miners. Indicates the current mining income and also provides links to distributors selling ASIC hardware.