Please don't block ads
I was reading a conversation recently which, whilst actually concerned with another subject, derailed a bit to talk about gmail. It was a typical desktop app vs. internet app and one of the things that someone was complaining about was advertising on internet apps (an argument which I do not see myself). To my horror someone suggested that you simply remove the advertising.
Now, I'm against blocking ads in general, but it does depend on the manner in which you block them. But to block google ads, to my mind, is simply ridiculous. Especially on gmail, a service that google provide for free. It costs them a lot to run it (this article [interesting-people.org] suggests that storage alone costs $6000), and they manage to keep it going primarily through advertising (note: I do know that the method used to remove google ads currently does not cost Google money - see below - but it is the principle here).
Admittedly some adverts on the internet are blatantly over the top. They are huge flash animations with sound that pop out of the page and play a full screen movie with a tiny teeny close button that's impossible to click. That's no exaggeration, I've seen quite a few just like that.
And because of this I can understand, to a degree, blocking flash ads from appearing. They are over the top. Static image based ads I understand less, they're not really that distracting. But google ads, I find to not only be non-intrusive if laid out right but also, because of the way it is done, actually relevant.
So if you want to block flash ads I won't hate you too much. But what really worries me is that the latest versions of the Firefox plugin Adblock actually let you not only prevent elements from showing, but also from downloading. Stop it from showing, fine. You're being a bit of an arsehole but you are still letting the host getting their money from it. But to stop it downloading you are simply stealing their services.
Okay, so stopping it from downloading costs you bandwidth. But you could be costing the host money. You are effectively forcing them to pay for bandwidth for you. But ooh the shame on them for getting you to enable them to get the money together to pay for their bandwidth so you can use their services.
If a site you use regularly has obnoxiously large flash ads consider persuading them to move over to something like google ads. If they still don't, then stop using their service, don't steal it.
Adblock currently defaults to removing ads. I would implore you to change the settings, if you must use Adblock, to only hiding the ads.

Comments
The companies that prevail will always find new ways to make a profit if their current business plan isn't working.. and the one's that can't adapt well enough to the current circumstances will just be replaced by companies that do. The whole system is built on growth and maximizing profit by any means neccesary and blocking some petty ads in your browser sure as hell won't stop them.. coz people got mouths to feed! :)
Any ad is over the top imo, not just those huge flash animations that you describe. I've never clicked an ad in my entire life and I never will so does it really matter if I choose to block them? The people that installs Adblock are clearly not big fans of clicking ads anyway so I really don't think the companies loose alot of money because of them. After all, its when a company sell their products or services through their ads that they make the actual money from them and not really when they get downloaded to my browser right?
But on the other hand stopping them from downloading means that the website doesn't get any money from that ad when you view the site because, as far as the advertisers are concerned, the ad hasn't been shown (which it hasn't). This means that the website is losing money because they are not getting the revenue from the ads each time you view the site (regardless of whether you would have paid any attention or clicked on it) - effectively in these cases you are stealing the services.
I do not believe that companies will find new ways, primarily because currently not enough people block the ads. They might be making enough to stay afloat, but that's like saying it's okay to steal from supermarkets because they have enough money. Also bear in mind that many of these aren't big companies, they're small time businesses or individuals just trying to get the money together to provide the service for the enjoyment of it. They don't really have the resources to go any other route other than advertising.
The only other real alternative I can see is to make people pay for the services from the offset (i.e. no free with-ad options) which is clearly undesirable.
Unless you can think of another way.