I am upgrading from the Canon PowerShot sd300 point and shoot camera to an entry level digital SLR. Could you point me in the right direction as to manufacturers and models that I should consider taking a look at?

Welcome to the Forum! I don't know of any new DSLR's in that price range, so you might have to look for something used, or wait till you can save a bit more money. As new models come out, people will be selling their old gear to upgrade.

I'm a Canon shooter so I will mention some of their stuff, but Nikon or any of the other manufacturers are sure to offer very similar equipment.

You might be able to find a used Digital Rebel (D300) in that price range or for an extra couple hundred bucks get a new one. You might also look for a used D60 or D30. I don't know anything about the D60 & D30 tho. Just know that their out there.

Good luck with your search!

Much like Michael pointed out...there probably isn't much in that price range, unless you find it used...I've been looking because like you, I want to upgrade. However, many entry level kits are starting in the $700-$800 range, so if you could find a couple hundred extra, you'd be in good shape. Good luck and welcome to the forum.
Ken

I bought new olympus e300 for less than $600 with 14-45 lens. Maybe it's not that good like canon / nikon but it's more than enough for me.

I didn't realize that the E300 was priced that low. Olympus has put some really neat features into their DSLR's, like that sensor cleaning thing. I'm a little concerned about the future of the 4/3 format - in terms of building a lens collection.

Other than this, you'd be looking at a used camera or waiting. The price of entry-level DSLR's keeps dropping, but it might be awhile before they hit the $4-500 range.

I bet you can find used Canon EOS 10Ds for about $500. With the EOS 20D hitting the used market, I doubt that 10D's are selling for very much. I've been thinking of selling mine and I can't see asking more than $500.

Looks like the new Digital Zuiko lens portfolio is filling out some;

http://www.olympusamerica.com/cpg_section/product.asp?product=1140&fl=16

Nikon just announced their new D200. Pretty soon you'll find used D100's selling for nothing (comparatively, probably in the $500 range I'm guessing). The D100 is basically the Nikon equivalent of the Canon 10D.

No matter what brand you go with, you're starting to build a system. Consider the lenses, accessories and features that brands are known for, and decide what to do from there.