What is the biggest cell? This turns out to be a difficult question to answer, which does not mean the Phactor cannot provide an answer. My initial thought was a slime mold, the real life blob! A bright yellow one crawled out of its petri dish and into my desk drawer once. A slime mold is an amoeboid organism that crawls forward by shifting its cytoplasm within a flexible cell membrane. This particular cell was about 10 cm across.
But while thinking about this question for a couple of days another answer came to mind after I happened to glance into the salt water aquarium down the hall. Growing there is a spectacular organism, a green algal seaweed called Caulerpa. As it's "stem" grows along it makes 4-5 cm tall "fronds" and rootlike branches grow down into the sand. They can grow to a meter or more in length. And believe it or not this organism is all ONE CELL! Now of course this violates classic cell theory, but organisms are notorious for ignoring biology. Larger size and a complex form is supposed to follow from multicellular organization. This green algae has many nuclei, lots of chloroplasts, but there are no cross walls dividing the organism into individual cells. So there you have it campers, the biggest cell is a unicellular green algal seaweed.
One sad note, this particular seaweed has become an invasive pest in some areas and it got to these places after being dumped from peoples' aquariums. That's a no-no folks. No releasing exotic organisms into the wild, ever.