Sigma has been putting out rather good lenses for the last few years. In particular, their Art line of prime and short zoom glass are very good value for the money.
They have also gotten into Cine High Speed zoom lens and Super Zoom lens as well. As my readers know, Sigma and Tamron are third party lens manufacturers. They 'reverse engineer' Canon and Nikon cameras and manufacture after market lens that fit these models. However, sometimes there can be minor hiccups and Canon and Nikon keep trying to outsmart the 'imitators'.
For those who want to save some money and perhaps get a lens that has different focal length from what Canon and Nikon offer, Sigma and Tamron may be a good alternative. For those into wildlife photography, there is a good deal on eBay for the Sigma 150-600mm f/5-6.3 lens.
Many Sigma lenses sold in Europe will go up in price rather substantially at the beginning of 2017. The list above shows the old and new dealer prices for some lenses. Check the latest EU prices on Amazon.de or Amazon.fr. Price increase for Tamron lenses will not be far behind either. If you are planning to buy one, better hurry up.