While you'll probably get recommendations on several different products with price points that will also vary, the manufacturer does recommend the use of petroleum jelly as their lubricant of choice for the O rings used in Maglites.
Some that withstand most anything will be killed by lithium based products. Ask me how I know this. I had some lithium grease destroy a $300 mtn bike fork.
I've got a mag that's 20+ years old and vaseline is all I have ever used on it, no problems at all!
Yep I concur that vaseline works very well on maglites. I woudn't recommend any which are in spray form as the finishing on maglites are very smooth, therefore using light/thin liquid type greases would eventually seep/creep out from the threads etc making a mess. Also usage of lites promotes heat which will effect the lube. In this case bearing grease which is thick in nature would be ideal and can be found at car workshops or DIY stores.
I've used Vaseline, black moly bearing grease, normal red bearing grease, bag balm, dielectric grease, or whatever else is handy, for over 15 years on various Maglites. Never had a problem, never destroyed an o-ring.