Answer: Trypanosoma cruzi
It is important not to forget about these extracellular parasites when screening a blood smear for malaria parasites. This image shows the motile trypomastigotes of T. cruzi. Note that these organisms are approximately 2-3 RBCs in length, and contain a nucleus and kinetoplast (below, arrow). T. cruzi can be most readily distinguished from the trypomastigotes of Trypanosoma brucei by the size of the kinetoplast; the former is much larger and appears to bulge from the organism.
An interesting tidbit: Contrary to expected, the kinetoplast is at the posterior end of the organism, while the flagella is at the anterior end. The trypomastigotes move with their flagella at their front.
Thanks to the four folks who wrote in with the answer - all correct!