These are why your photos aren’t as good. These are very basic things they should have taught you in class before they hand you the camera. Again like everybody said it’s about knowledge, not cameras as you said yourself, people do great with the same camera you have. Instead of saving money for a new camera or even new lenses, put that energy into learning. Get books of "how to" or "the best of" from the city library. I’ll hand you a D3 and talk my boss into letting you use his portable $15,000 studio setup right now. But if you shoe flash someone at 17mm, the picture will look bad. I’ll give you my C3 from 1951. And it will still be the same.

You may have talent but if you don’t know what your doing your pictures will suck. The mentality of thinking some new thing will give you good pictures is what your problem is. Learn, and then your pictures will be good.
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invest in lighting and learn how to use it before getting an upgrade if your serious
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If you’re only using your kit lens, you’re limiting yourself a lot. If you’re on a tight budget, look at the Canon 50mm f/1.8. It’s about $110, and optically it’s miles ahead of your kit lens. If you’re ready to invest a bit more into your business/hobby, get the 50mm f/1.4 instead. Optically, it’s better glass, and the build quality is far superior to the f/1.8. Also check out the 85mm f/1.8 for tight-in shots.

Don’t worry about getting a 5D Mk II just yet; get some quality EF-mount lenses first. That way when your business starts making you money, you can upgrade camera bodies as needed.

And… I’m glad that you’ve learned how to shoot Manually, that puts you miles ahead of most people who consider themselves "photographers." However, a 20 megapixel camera does not take any higher quality images than a 12.2 megapixel camera. Megapixels determine ONLY the size and dimensions of the photo, and have NOTHING to do with quality. Likely what you’re seeing with professional photos taken with the XSi were using high-quality lenses.

If you want to replicate an image like this, for instance:

http://www.flickr.com/photos/naturesmugshots/4823108736/

You need to shoot for a few things:
-Shallow DoF (this is very easy to achieve using any of the lenses I listed above, you should know how)
-Good composition and posing
-Retouching (I used Lightroom; the "Skin Soften" adjustment brush does wonders for those who know how to use it)

Frankly, I think the biggest thing you’re not seeing in your photos is really soft, even lighting, and professional-quality retouching. Practice both of them.
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Pro photographer, camera store employee

A good place to learn about off camera lighting is the Strobist blog;
http://strobist.blogspot.com/2006/02/welcome-to-strobist.html

Starting with small, manual speedlights can be a great way to learn how to light. As photography equipment goes, they’re not expensive (a manual flash can be had for £40 and a set of radio triggers to fire it off camera for £27) and just one light, off camera, can dramatically improve your shots.

Remember, its not just about light, but about shadow too – and using both to portray a 3D object on a 2D medium. With off camera flash, you can control its directionality and shape & mould it – that’s light control!
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If you are taking dull pictures with your camera, then its NOT the cameras fault.
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you could buy a 5D Mk II and still suck at taking photos…

if you haven’t learned the basics, then don’t think that an upgrade will help…
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http://photo.tutsplus.com/articles/round-ups/100-helpful-photography-tutorials-for-beginners-and-professionals/

lens help, but photoshop helps more…

http://www.youtube.com/watch?v=_HGvDNpClls

check out other vdos too..
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