I think plants offer some of the easiest to understand and experimentally reproducible evolution work. A good book to start with is Karl Niklas' The Evolutionary Biology of Plants. Botanists estimate that 20-40% of existing plant species have arisen through a process of hybridization, a process not normally available to animals (but who knows?). That is an astounding number and several plant species have been experimentally derived from known wild plants through a plant hybridization process and the produced species are identical to known wild species. The rapid life cycles of plants compared to animals is a big advantage.
Here's a shortened paragraph (p64, Niklas' Evolutionary Biology of Plants)
"One of the most stunning "laboratory" investigations of speciation is that of Loren Rieseberg and his coworkers, who reproduced the genetic changes leading to the formation of a naturally occurring species of sunflower (Helianthus anomalus)......Under laboratory conditions these changes are repeatable across independent experiments....The two putative ancestral species of H. anomalus are H. annuus and H. petiolaris. All three species are self incompatible annuals....hybridized H. annuus and H. pertiolaris to produce three independent hybrid lines that were subjected to different sib mating and back crossing regimes......lines converged to nearly identical gene combinations including parallel changes in the nonrearranged portions of chromosomes.....the path of evolutionary change was repeatable in ways suggesting that selection rather than chance governs the genetic composition..."
Sorry about hacking the paragraph so much, but there are copyright concerns. If you have access to Science, here's a reference:
Science 28 November 2003: Vol. 302. no. 5650, p. 1499 DOI: 10.1126/science.302.5650.1499