What are some of the most reputable tools for doing this? Something that many users have used for years without issues.
https://iancoleman.io/bip39/ has been around for several years, popular, and trusted. Just check the "Show Entropy Details" box at the top and you can input your own entropy including dice rolls and/or playing cards.
Thanks! Yeah, that's one I came across too that looked trustworthy. Great to have this independently confirmed here.