Evolution can be seen to happen over fast breeding complex organisms, such as insects, and even mammals if the experiment time is long enough.
I wish I could remember the study, but in Highschool (a religious based school no less) our science teacher showed us a doco that cited a study that took place over 25 years using rats.
The rat were separated from their food by tunnels that were fully submerged, and would have been pushing their lung capacity to get to the other side. The rats could clearly see their food through the glass, but had to get to the other side through the tunnels under water.
From first to last generation, the rats eventually lost all hair, their lung size markedly increased, and their paws developed webbing...
I don't know what clearer proof of evolution you could ask for.