Claire
Depends what you want to do with your photography
The camera you have is a 'point and shoot' camera, and is fine for general snaps etc. But you are unlikely (but not impossible) to take really good shots consistently with it.
Next step up is a 'bridge' camera, so called because it bridges the gap between point & shoot and proper SLR cameras. Bridge cameras are fine and have a lot of the features of SLRs, EXCEPT you can't change lenses. They can suffer from poor lens quality (which you will eventually notice as you get better). Prices vary, but I bought a Fuji 9500 (now 9600) for abot £280.
Last stage is SLR, where you can change lenses and have much more control over settings, add filters, and do all sorts of stuff that you can't with the others. There are plenty of price options, but the Canon 400D is a very good starter. The 450D is the latest, but its more expensixe because it's new, and isn't really a big improvement. Have a look at this site Warehouse Express,
Cameras & Lenses - Cameras - Digital SLR - Warehouse Express
they are pretty cheap. The 400D is about £400 with a basic lens, and you can buy better lenses later and interchange them. Nikon are good too. If you buy a new camera, you might want to go to an experienced camera shop first and ask advice and you can feel and try the cameras. You can always buy elsewhere. With SLR it's mostly about the lens, not so much the camera.