Firefox, Opera, Konqueror, Safari. Some of the seriously advanced (standard) stuff aren't even supported by many of these generally-good (when it comes to standards) browsers, but if you're using seriously advanced stuff then obviously it's a seriously advanced page you're making - feel free to alert users that it won't be rendered, and feel free to refer them to FF/Opera/Konq/Safari or whatever good browser WILL render the page (if they're visiting the page, it should be safe to assume they want to see it. When you alert them they can make their minds up if they wanna install FF, install Opera, install GNU/Linux (for example) + Konquror or buy a Mac (so they can use Safari)).
The main point is if you want 90% of people to be able to view your page then don't do any advanced stuff most browsers won't work with as few people will change just to view your site, they'd rather go somewhere else.
I found a really good answer to the question "Why are standards so important?", from the dillo web site (lots of good (as in good) stuff on that site:
I agree standards are very important, in every aspect of technology, including hardware too.
BTW I used to use an extension that would persist Firefox. If the electricity went off, or something crashed, starting FF would just continue it like nothing happened. If I had the extension installed now and the power went off, once I run FF next time I'd still have my post infront of me. There is one problem that I heard about it though (never affected me though) - apparantly you can't install other extensions with it on (that's why I'm not installing it yet, until this is fixed).
Sounds handy, don't think even Opera supprts that, how about the contents of forms, if you were in the middle of typing a post would you loose it if the power went off?
One of my favourite reads ever
I'd rather not derail this thread so I'll be as brief as possible.
I found this article difficult to read he does bollock on a bit but none the less he does raises some valid points but I don't buy into all of them.
Like the economics of free software for example, he's obviosly thinking about operating systems and servers where the author can easilly make a profit on selling their services. However this doesn't transfer to other areas like computer games, (no one's going to play each level over and over until it's bug free) this is why open source software hasn't done very well in this area. I think free software is great but it isn't suitable for all business models, it depends on the type of software you're selling and the market you're aiming it at, saying there's only one way to do things is a very bad thing.
What about pattents?
We all bitch about software pattents but no one ever bitches about hardware pattents. From Stallman's point of view if you copy someone's invention and then start manufacturering it yourself you shouldn't be hurting them (I don't agree with this). There are serious implecations for hardware pattents, the main ones are storage media and protocol, it's the same principle, stopping the competing product interoperating with yours.
As far as I'm concerned pirating software is bad but it's not as bad as the companies say. Stealing software is like sneeking onto a bus or train or into a cinima or concert without paying or even watching cable TV with an illegal decoder, you're taking away their business.