Here are my opinions on the various AF brands. I've tried to keep things breif, so if you have any questions or comments, please feel free to contact me.

A general note on Entry-Level AF SLRs:

     Looking for a good camera? You might want to think twice before buying any of the entry-level models. While they are a step above a point and shoot, they aren't really very good SLRs, and if you are at all serious about photography you will outgrow one of these cameras in six months or less. This includes the Canon Rebel, Minolta 400si, Nikon N60, and similar cameras from other brands. Why do I feel this is the case? For a number of reasons.
     First and foremost, the construction quality is quite low, as everyone is trying to make their camera smaller, lighter, and cheaper than everyone else. The Nikon N60 is the best of the current entry-level cameras, but it costs more than the others and even it doesn't have nearly as good construction as the N70 and other higher-end bodies. The entry-level cameras have so much lightweight plastic that they are easier to break, and simply do not have the potential to last a long time. In fact, I have seen point and shoot cameras that cost far less than an entry-level SLR and offer far better construction (take a look at the Konica Big Mini to see what I mean).
     Second, the entry-level cameras don't really have good features. They have the basics, but that's it. There are very few additional features or options to allow you to get into more advanced photography. Also, the way the cameras are built, you often get mirror lag. This means that after you press the button, the motion of the mirror prevents the shutter from firing immediately. The picture is actually taken a half-second or so later. How much difference can that 1/2 second make? If you're doing ANY sort of action photography, it's the difference between getting the shot and getting absolute junk. In a recent issue of Popular photography, a woman was complaining about this very problem with her point and shoot, and I find it unforgivable that similar shutter lag problems exist in the entry-level SLRs.
     Finally, the point of getting an SLR is to get a better camera than a point and shoot. However, with the lackluster construction quality and limited features, spending $400 or so on an entry-level SLR doesn't give you much better quality than a point and shoot. Yes, you get interchangeable lenses, but that's all.
     So my opinion of the entry-level cameras is this: If you want a point and shoot type camera that you can change lenses on, then the entry level SLRs such as the Canon Rebel are a great buy. However, if you intend to do any sort of serious photography, buy an upper end model. If you don't, you'll only lose money when you outgrow the entry-level camera and upgrade to a better model (and believe me, you can outgrow one of the entry-level models after only six months).

Canon - One of the largest and most complete AF lens systems, and all the bodies offer a large number of features for the price. However, I don't like the way the consumer end equipment is getting increasingly junkier - more plastic, lighter construction, more gimmicks (Eos 3 - 45 focusing points, need I say more?), and plastic lens mounts on the low end zooms is now standard. That being said, I still think Canon offers a great AF system, and I have been very pleased with my EOS equipment and I think they have one of the best systems on the market, particularly if you get into the higher end equipment (A2 and above).

Nikon - Excellent quality cameras. The lens system is impressive, and the ability to use older manual focus lenses on AF bodies is one of the advantages of the Nikon line. Nikon has also done a bit better job keeping overall quality up, and the N60 is a bit better built than the Rebel and other entry level cameras. The downside - higher price. Part is due to the fact that overall quality is a bit better than the other brands (except for higher end Canon which is on par with Nikon), but also is undeniably due to the Nikon name for which they charge a premium.

Minolta - The system used to be quite lacking, but Minolta's recent introductions (both new bodies and lenses) has done much to improve things. For those who don't require access to a complete line of professional equipment, the Maxxum line is quite extensive and offers much for snapshooters up to advanced amateurs.

Pentax - Getting better, but still lagging behind all the other brands. The new bodies are nice, but Pentax does not offer any high-end or professional bodies. As far as lenses, the system has been expanded recently but it is still quite limited in comparison to the other three major manufacturers. However, Pentax AF bodies do accept K mount lenses, so those with older Pentax bodies can move to AF and still use their old lenses. Like with Nikon, this can be an important advantage, but as a pure AF system I'm not particularly fond of Pentax.