Beware of Baen. They're demonic. They'll give you the first few books in a series free ... and the next thing you know, you've got a huge dent in your wallet and a corresponding bulge in your TBR list. They're the crack dealers of ebooks. I'm trying to stay away from there until I get through the
last stack of ebooks I bought from them. I won't manage it, of course, because I've got so much to read, and Baen has so many new books coming out, but I keep promising myself that this time, I'll just look at the upcoming books list, and not drop another $50 on books. If I try that enough times, maybe I'll eventually succeed.
All tongue-in-cheek warnings aside, Baen is doing everything right. I've been buying their books on dead trees as long as there has been a Baen Books, and now I'm buying almost entirely ebooks from them; they're cheaper, and don't require a visit to that dangerous place called a physical bookstore, where other books can ambush me and insinuate themselves into my hands. Their politics make me itch, but that's another matter entirely. What matters is that they treat their customers like honorable people and valued customers, not presumed thieves and enemies. They deal fairly with me, and I give them money; win/win.
Afa, just grab yourself a copy of calibre and use its built-in reader. You'll need it anyway when you get your ebook reader, so you might as well get an early start.
Also, the Baen Free Library has an adequate online reading feature. I second the recommendation for the Honor Harrington books, though I think the series jumped the shark a few books ago; "the Salamander" has become something of a Mary Sue. I'm looking through what I have tagged "Baen Free Library" and noted Ryk Spoor's Digital Knight -- good book; I have that on dead trees too. David Drake's Old Nathan is great, and try Rick Cook's "Wizardry" series. Some of the following are in the BFL, some are on the CD archives, but all are online free: try With the Lightnings, Fiddler Fair, The Tank Lords, and Med Ship. There's probably something in there you'll like.
Unless you're a hardcore Tea-Partier, you'll probably want to avoid John Ringo and Tom Kratman. Unless you're fond of being repeatedly hit in the face with exhortations to protect children, you'll probably want to skip Mercedes Lackey's "SERRAted Edge" stories (but only that series). But that's what's so awesome about the Baen Free Library: you can read 'em, and find out of you like 'em or not, before you shell out actual cash money.
The Baen folks are smart: they know a lot of people won't take a chance on an unknown book or author, so it's not a lost sale to give the books away; for every sale they lose to someone who might have bought the book to see if it (or its series) was any good, they probably get ten from people who wouldn't have bought from them at all if they hadn't read the sample, who buy the whole rest of the series.
In a time when publishers at least claim to be struggling, Baen has been thriving. They're far from the only publisher of SF and fantasy, so it's not their content. It has to be -- it can only be -- their business model: treating customers well, offering a good product at a fair price, and giving out free samples.
And I'm proud of myself. I didn't buy the first two of the Complete Hammer's Slammers series (because I'm hoping for a bundle discount when #3 comes out, but hey, I at least postponed it!)