These sites I find really helpful.
Some reference images like these are useful if you’re unable to find/join a life drawing class. Though I would highly recommend going to one:
Eadweard Muybridge photography is very helpful in understanding the body in movement.
Male Anatomy Reference Post
For Anonymous, who requested more Male Anatomy related things.
There are quite a few male related anatomy items in the Art Resource but the search function is a bit persnickity at the moment. I will try and update this post as I get more references. If you’ve got any that I don’t have here, go ahead and put them in my Ask and I’ll update this post.
Kakimari’s Anatomy Dump - This one seems to be for the most part geared towards male anatomy. Everything you could think, legs, arms, feet, hands, necks, shoulders. A nice thorough study that’s really helpful!
Anatomy Study based on Steve Hampton - Some demonstrations on how to stylize anatomy, lots of masculine examples.
Manly Butts - Can’t explain it better then that. Butts.
Manly Legs - Lots of studies of different leg positions.
Hands and Feet - Can quite easily be unisex.
Hands - Another hand reference which could be helpful.
Loomis - Andrew Loomis, basically the patron saint of Anatomy. All his books are here, including extensive male, and female anatomy.
How to Draw Beef - Everything it promises to be~ Aka: fantastic. Great references for muscles, different body types, ect.
Dicks - How could I almost forget all these cocks.
Feet - Feeeeet.
Neck and Shoulders - As it says, some nice neck and shoulder references.
Different Male Bodies - Good resource for a few different types of bodies that are still pretty aesthetically pleasing.