I'd like to know if there is a way to scale down images to a set size in px, but WITH maintaining aspect ratio because not all images are square. Say to make the image fit a frame of 180px by 180px.

Also it should be compatible with all browsers.

I know that

img {
width: 50%;
height: 50%;
}
Can give a workable solution. However I need a foolproof one in case the image sizes are significant;y different, or if the images are the correct width as they are and this css just reduces it to half for no reason.

If you are planning to have different images re-sized, why not use HTML height/width attributes :

<img src="IMAGE" height="50px" width="50px" />

It's perfect for re-sizing a lot of images on your web page with different sizes,

it's a database driven site.. images vary in size from 150px to 300px in width, also shape as well.

The images need to be tiled in a 3x3 format, so I'm looking for a way to make the images uniform to look good on the site.

do the css needs to be like a catch all system that will resize all the images at the user end, hoping there is a css fix out there, because I don't want to spend a fortune getting a programmer to fix the php system to make the images a certain size to begin with.

You can try css parameter max-width in percent value.
Something like this:
<img class="imglow" src="/images/image.jpg" />
.imglow {max-width:30%;}

http://unstoppablerobotninja.com/entry/fluid-images/

I already tried this solution for my blog and working fine

img {
max-width: 150px;
}

I think not need to add height, It will taken as per proportion