Gamewise, anyway. Insofar as the canon-ish stuff goes, just about anything can be used to kill force users -- plenty, even very strong ones, are killed in straight up 1v1 situations by non-force sensitives with a blaster or just whatever, nevermind things actually stacked against them or fun stuff like orbital bombardment -- it's just significantly more difficult than it would be against someone that's not a trained user. They're quite kickass, but there's a reason armies and special forces and whatnot still exist in a universe crawling with force sensitives and other weird stuff.
And yeah, there's stuff in the universe that just flat no-sells lightsabers and most direct force counters (dodging or TKing the weapon itself might still work, ferex). Pretty sure sonic weaponry worked like that, amongst other things. The sabers and force sensitive critters get played up more than a little due to narrative, honestly. Y'gotta' remember that jedi got slaughtered pretty much en masse by freaking droidikas, nevermind the stuff that was actually vaguely competent. Impressive buggers, pound for pound, but most of their really notable work was via social-fu and whatnot. Even a lot of the sith stuff was about non-combat (or at least combat-via-proxy) applications. They were at their best as force multipliers rather than direct combatants, more or less.