I use myhairdressers.com and scissorboy.com quite a lot. Almost an addiction, lol.
Myhairdressers has a membership fee and scissorboy is free.
If you sign up for the free week trial on myhairdressers, you've nothing to lose and they usually offer you a discount if you subsequently decide to join.
The myhairdressers guides you through the entire process, (from head block basics to more advanced cuts, colours, hair up etc.) in detail and is probably particularly suited to newly qualified staff and trainees.
(They are advertising that they're offering a special package for NVQ level 2 students soon, which might be especially helpful for students in colleges without a salon placement.)
Scissorboy.com has lots of useful short videos featuring a wide range of salon professionals from across the globe. It's great for inspiration and tips but perhaps not so well suited for trainees as it glosses over some of the details.