Restocking or reselling is what many users swear by - with a fast connection and plenty of practise hundred-thousands to millions is not unheard of in a very short space of time.
The Stockmarket apparently is also not a bad way to make some neopoints if you know what you're doing or alternatively if you have the patience and just sit and wait until the price eventually rises (with the exception of when a stock goes bankrupt prices do rise again at some point).
Random events, dailies and games are the other ways to gain neopoints and it is probably something that I do the most of (not a fast enough connection for restocking and I don't stay dedicated enough to the stockmarket). With respect to getting neopoints this way its all a matter of patience, unless you get
really really lucky you are unlikely to ever have hundreds of millions but with patience you can build up a few million.
Of course, it is also possible to make neopoints via a combination of all three