Random.org
True random numbers from atmospheric noise, not a pseudo-random algorithm.
Most "random" number generators are seeded pseudo-random — deterministic under the hood. Random.org instead samples atmospheric radio noise for actual randomness, and has done since 1998. Free for the core generators (numbers, list shuffling, coin flips); the paid tier is aimed at researchers and lotteries needing certified randomness at scale, which most visitors will never touch.