Having just gotten into them myself, about a year and a half ago, I have come to find out there aren't a lot of things that can be considered graphic novels. Most are comics. However, they do package these up in trade paperbacks so it gives an appearance of a graphic novel. These can be found at Amazon.Com for $10-$20 depending. (Or pay more, but do good by supporting your local comic book shop!)
If you are NOT into superheroes, then a good place to start would be the publisher Vertigo. They are a subdivision of DC Comics. Vertigo has a lot of great series and as far as trades go, they are usually cheaper then all others. I have been reading "DMZ" by Brian Wood. Very good, in my opinion. If you are a fan of urban/modern fantasy, Neil Gaiman wrote the Sandman series. On the more sci-fi side, though not really heavy stuff is "Y: the Last Man" by Brian K. Vaughn. These are all from Vertigo. DMZ has 8 books out, with the 9th coming in late February. Sandman and Y are both 10 book collections and completed their runs. Not what you were looking for, I know. I haven't hopped on any that recently started, other then one. That one is "Cowboy Ninja Viking" and it's out on Image. Can't remember the author's name. The second collection just came out last week.
Some obvious choices that seem more of a graphic novel are "Watchmen" and "V for Vendetta". I highly recommend both. And one that comes as either three graphic novels, or you can buy the actual omnibus edition is Jeff Lemire's Essex County stories, which was excellent. I am sure others could point you in the direction of material out there that is a graphic novel and not just a collection of comics.
