There are many Warcraft novels on the market. Are they a good source of canon lore, and if so, in what order should I read them in?
You're going to get mixed answers on this one, so perhaps our readers will give you a second opinion on it after my answer. Speaking strictly of the novels, I definitely recommend Beyond the Dark Portal, Rise of the Horde and Lord of the Clans. That's the order I would read them in, but any order should be fine. They're specific points in history, but there's enough of a gap between them that chronological order isn't mandatory. They weren't even written in that order, so it's no big deal.
I don't personally enjoy Richard Knaak, but Day of the Dragon is worthwhile simply because it sets the stage for a few things and gives you a little bit of understanding of why the Red Dragonflight and the Kirin Tor are buddies up in Northrend beyond "the Blue Dragons are killing our mans." Plus, it's one of his earlier Warcraft novels, so Rhonin isn't a complete joke in this one yet.
I would not read the other Richard Knaak novels if you're looking for anything canon. The War of the Ancients is an event that happened in Warcraft lore, but Knaak's telling of it in the War of the Ancients Trilogy is not entirely canon, according to a Community Manager's post on the WoW forums sometime back. If you've read Richard Knaak before and enjoy him, by all means, give them a read. I really am not a fan though, so I'd personally say give that trilogy a pass. If you do read it, reading Day of the Dragon first may be wise, but not mandatory. The trilogy takes place after that and heavily uses Knaak's own characters, rather than Blizzard-made characters, so they're not something you would have learned about in WoW or the other Warcraft games.
The rest of the novels are sort of take it or leave it. They give you a good background of the lore, but I wouldn't call them must-reads. I recommend them, but you won't die if you don't pick them up. Cycle of Hatred in particular was not something I would read more than once, but I am glad I read it that one time.
I wouldn't tell you to not read any of them, but some are definitely much better than others. The War of the Ancients trilogy is decent fan service if that's what you're into, but the events are non-canon and it's so gratuitously fan-servicey it makes me a bit ill. The rest is up to you.
They've done a pretty good job of making the various novels independent of one another, so you don't need to read them in chronological order unless they explicitly state which order they go in, like the aforementioned trilogy. Don't worry about what comes first otherwise. Pick out whichever ones look most interesting to you. Wowwiki has a full listing of all of the current Warcraft novels.
By the way, for those of you that have read all of the Warcraft novels already, are you as excited about Arthas as I am?
You see Burning Legion teleporters all over the place, bringing in demons from the Twisting Nether. Why did Kil'jaeden have to be summoned through the Sunwell? Couldn't he just step through one of the teleporters?
It's possible that it's just a story hook that they used for Killy J, but there's some history with this sort of thing in Warcraft. The bigger the demon, the more juice it takes to summon them. For example, in the War of the Ancients, Sargeras had to be summoned via the Well of Eternity. During the Third War, Archimonde needed Kel'thuzad to arrange a special ritual to bring him to Azeroth. Kil'Jaeden is pretty darn powerful, considering he's the current head of the Burning Legion with Sargeras out of the picture. Regular Legion teleporters can't handle the big dogs, I suppose.
I went back and read the article about The Scythe of Elune, and it reminded me of all those book I pick up for my hunter in Kara, The Torment of the Worgen, and the Singed Page you receive after using it. Is there any lore indicating who wrote those books in Kara or who they are about? I'd be very interested to learn about all 4 of them (not just the Worgen) if there is any info out there about them.
As far as I know, those aren't retellings of any 'real' events that happened or have any connection to anybody. They use 'real' concepts like the Worgen, the Titans, et cetera, but they're just stories. Works of fiction within the work of fiction that is Warcraft. Epic tales of gallantry or horror or whatever. They're really cool, but I don't think they're meant to be much more than that. It's just really, really cool flavor used to deliver a fun buff.
Zachary Hill asks...
I don't know if this truly counts as a lore question, but I was wondering if Blood Elf Death Knights would be called something special, since they are technically not Paladins, but Blood Knights. And looking at the lore from tabletop games such as Dungeons and Dragons, a Death Knight would be basically a fallen paladin. I back this up in WoW lore with the Wrath of the Lich King teaser, where the first death knight (can't remember the name, Arthas?) changes from a paladin to a DK. After he "falls" no less.
Not all Death Knights are fallen Paladins. A lot of them are (and Arthas was) but not all of them. The Scourge is not especially picky about what you were in life. They only care about your capabilities. If you're strong, you can become a Death Knight, no matter who you are. If you're not strong, you'll probably be used as a ghoul or some other fodder.
So no, Blood Knights do not get a special name as Death Knights. A Death Knight is a Death Knight. Paladins may be prime candidate for Death Knighthood, but that's the extent of it. Warriors, Rogues, Farmers, they could all potentially be Death Knights.
Why do Gnome NPCs sometimes say "Daylight's burning!" as a greeting? Seems somewhat odd for a generally cheerful race. A reference to Gnomeregan, or because they lived underground and now they're scurrying up top with all the other races, perhaps they're a little photosensitive?
Well, heh, I don't think they mean it in a "Your star burns!" kind of way. It's an expression that means something like "you're wasting time!" Sort of how Goblins say "Time is money." Hurry up, don't dilly dally, that sort of thing.