I recently picked up a Eulophia petersii that hasn't bloomed yet, but I understand they can get
quite tall.
One of the most noticeably long spikes I've seen in person was this phalaenopsis (I think?) that bloomed recently at the Huntington Library in San Marino, CA. The plant itself was a small thing, possibly mottled-leafed, and mounted to tree well above my head. If I recall correctly, the spike holding these flowers was a compound one, the total length being somewhere between 3.5-5 feet I'd guess. Perhaps someone else can identify it. Unfortunately, I seem to be lacking a wide photo of the stalk or anything of the plant itself.