I didn't really become active until last year, so I apparently missed out on the "golden years" but here's a few people off the top of my head.
Seece - He and Kowenicki pretty much represented the Xbox community. That and his sales analyzing threads definitely aided to his 'iconic' status. He wasn't the most peaceful poster, oftentimes lashing out at others. Nor was he the most unbiased - his console preference were well known. But I think that makes him even more memorable and iconic. Some people think he's gone, but I believe he lurks amongst us hidden behind an alternate identity.
Badgenome - He doesn't leave as many jokes now as he used to, but when he does, there still as funny as ever. He seems to be a master at one-liners and quick thinking - something I can only assume he learned after years of studying Youtube comments. He seems to have drifted almost exclusively into political threads recently though, so he's definitely less iconic than he used to be imo. But still, his one-liners are quite special.
Rolstoppable - He's pretty much dead these days but back in the day, but he was very significant here. His threads were the kind of threads that made you value a day spent on the site. I rarely agree with his opinion on gaming, but you can tell he usually puts in a lot of thought into his posts, usually resulting in a humorous outcome. His avatar and username comnbo definitely helps to instill his memory into people's memory, thus, causing an 'icon' image.
D21Lewis - Like Badgenome, he was defintely one of the funniest members on this site, if not THE funniest members. His style was a little different from Badgenome's, becuase his jokes were usually more drawn out into several sentences, or even paragraphs sometimes. The reason I keep saying 'was' is because, like the other members listed, he doesn't seem to be firing out the jokes quite as often as he used to. He seems to have grown out of VGChartz like the others.
Nsanity - He basically keeps the Xbox forums alive these days. He represents news. Some people have theorized that he's actually a robot built to spread Xbox news across the web. Seriously though, he actually posts a lot useful news threads about all companies. If it wasn't for him, I would probably miss out on about 40% of gaming news, considering this is pretty much the only gaming site I visit.
ethomaz - Simply because he's an icon of Gran Turismo and sometimes playstation in general. His bond with GT is stronger than any bond I've ever witnessed in my life. I can only imagine what he was doing on this site before GT5 released.
There are other posters that people mention like Darth, Soriku, etc. but my memory of them is too cloudy to make any statements.