If you aren't getting the kind of detail you can see in the first images, I would look at lighting / technique before looking at new lenses. The 50mm f1.8 in particular should be able to give you spectacular detail in a studio setting with the right lighting and post-processing. Even the 18-55 when stopped down should be able to give you acceptable detail for web work.
Are you shooting from a tripod? Are you trying to shoot with the lens wide open but with extremely high shutter speeds or something?
If I were you, I would spend some time practicing and experimenting. Set up your shot as if you had a model there, and shoot something that will really show differences in resolution. Maybe make up a board with a whole bunch of fabrics of different textures or something, and then shoot them, trying various combinations of aperture and shutter speed. Then examine them in dpp or photoshop to get a better feel for how your current lenses perform.
If you're not happy with the results, rent a really good lens for a day and run through the same steps.
Also, do you know how to sharpen and clean up your images in post-processing? Most catalog images have probably gone through some post processing, so if you're comparing what came straight out of your camera with images that someone has spent some time optimizing, you aren't really getting a fair comparison.
Canon 60D | EF-S 15-85 IS f3.5-5.6 USM | Tamron 17-50 f2.8 non-VC | EF 50mm f1.8 | EF-S 55-250mm f3.5-5.6 | 430 EXII