It depends on your budget really. If it's under £100, the only but good choice is the Canon 50 1.8 II. Build quality is not great, but image quality is good.
A bit further up the scale you can consider the Canon 50 1.4, but also the Sigma 30 1.4 and the Sigma 50 1.4. The Sigma 30 and 50 have better image quality than the Canon lenses in my experience.
If you want a longer focal length the Canon 80 1.8 is reputedly excellent and probably better than the Canon 50 1.8 and 50 1.4.
I have personally used the Canon 50 1.8, the Canon 50 1.4, the Sigma 30 1.4 and the Sigma 50 1.4. Allegedly, the Sigma 50 1.4 has the same design as the Sigma 30 1.4, but the 30 is for crop cameras and the 50 for full-frame cameras.