As Rogério says, for larger species, many figures by the major brands are useful. For smaller species, Japanese brands will be useable, and sometimes the smaller species in toobs and those by vintage brands. If you are strict about scale, don't trust the manufacturer's scale, as it is often wrong.
I collect in 1:32 scale, and I spend a lot of time measuring the figures on TAW and STS with a ruler on my screen, using size information such as Lego blocks, the Schleich man (45 mm with ring on head), etc.
It's time consuming to collect to scale, but also good fun, as you discover many different brands that you'd otherwise not look into. And while you look up the sizes of animal, you also learn a lot about the animals themselves.