I've got a very eclectic taste in knives, and I've dealt with many companies both as a blade junky and as a dealer. These are the brands that make up the bulk of my collection (all users, no safe queens).
-Victorinox and Wenger. The blade steel they use isn't great, but their fit and finish is top notch. I love both their Swiss army knives and multitools. Great value and what's probably the best warranty ever (no matter what the paperwork says, you send a broken knife and they return it fixed or give you a new one for free). No matter what else I carry, there's a SAK in one of my pockets.
-Spyderco. Great knives, good prices and excellent customer service. I like the way the Glessers run their company, I get a warm fuzzy feeling everytime I send money their way. And I'm not just saying this because of their FTF discount (search some of my threads from way before we got that deal).
-Kershaw. I like their designs a lot, and also love that they offer some very well priced American made folders (like the Skyline or Storm). I'm particularly fond of the models with composite blades, and while I'm not a die-hard assisted opening fan I find it entertaining.
-Fallkniven. Simple designs, quality materials, convex ground blades. The only thing I don't like are the rubber handles (but you can just get finished blade blanks and a couple of on-line stores offer custom handled versions). The F1 (with full cover leather sheath) is one of my favourite outdoors knives, while the WM1 makes a perfect fixed blade EDC. Their folders are great, too.
-Benchmade. Mmmmh AXIS lock... I wish I could still buy them wholesale from my distributor, amazing knives. I was introduced to this brand by an Aussie friend who sold me a customised Ares. I also like their balisongs very much.
-Fox. This brand isn't well known in the US, but they've made loads of stuff for well known American companies. They made the Hossom fixed blades for Spyderco, the Retribution folders (also a Hossom design) for Ontario, they make folders and pens for Mil-Tac, stuff for TOPS, etc. The knives they are making for the Fox Military Division line are excellent. I was sent a few samples to write an article for an Argentine magazine and liked them so much I ended up buying a couple.
-Great Eastern Cutlery. GEC is a relatively new company that's making excellent traditional folders. I haven't tried any of their stainless steel knives, but I'm really happy with their carbon steel ones. I'm definitely going to add a few more to my EDC rotation.
-Case. Their QC has had some ups and downs, but in the past few years I think they've improved a lot. I don't care for their "Surgical Stainless" blades but I'm crazy about their offerings in carbon steel (they call it CV for chrome vanadium). There's something special about the way a bone handled slipjoint with carbon steel blades ages, it's lovely. Hell, I've even taken a liking to some of Case's knives with yellow plastic handles. My yellow Sodbuster Jr. has seen more action than all my fancy tacticool folders put together, the CV blade is covered in a delightful patina. Probably the best $15 I've spent on a knife!
-Bark River Knife & Tool. Mike Stewart (BRK&T owner) knows a lot about knives, he was vicepresident of Marble's (and some people are willing to pay extra for Marble's knives made under him!). IMHO, these are some of the best production fixed blades in the market today. Sheaths used to be rather crappy, but that has been fixed. I love that they bring old traditional designs back to life. I don't have any experience with their newer tactical knives, I prefer their outdoors oriented ones. Mr. Stewart is to blame for my convex grind addiction.
Ok, by now it should be clear that asking me to pick just a couple of knife brands is impossible, I could go on and on and bore you to death. There are too many good ones out there and I'm sure that I'd find it easier to commit to a single woman for the rest of my life than to only a handful of knife brands.