jointhefediverse.net seems to be a commonly linked resource for directing people to join the Fediverse.
Curiously, it does not list Lemmy under the list of Reddit alternatives. Their GitHub README explains why.
Previous relevant discussion: https://lemmy.ml/post/78808
hm, raddle.me / postmill looks promising though. is it federated at all? i haven’t dived into the code enough yet but i’d love it as an alternative.