The consumer-level HD, while capable of 1080i resolution, is compressed, whether speaking of HDV or AVCHD formats (the two main HD formats for consumers at the moment).
The primary considerations for compression are file size (really large for uncompressed HD) and bandwidth, meaning the storage technology for consumers is not “wide” enough to accommodate the high data demands of the uncompressed HD format.
That said, the newer solid state storage devices are using an MPEG-4 based compressor, that is based on a collaborative between Sony and Philips called AVCHD, that most of the major manufacturers are adopting as a solution to the previous encoder, HDV (based on the much older MPEG-2 standard that DVDs are encoded with). As to the compression algorithm, the newer codec (AVCHD) is better overall, but comes in varying levels of bit depth; a lot of the lower-end camcorders are 12-bit, which really takes the picture quality down especially in low light and high speed photography. The Canon I mentioned earlier, while a bit pricey ($1000), is the least compressed version put there with 24-bit video (AVCHD has a max bit depth of 24-bit, so it’s the highest quality for that format).
Otherwise, above that level you’re getting into full unconpressed HD, which is considered pro quality in format and storage (a whole league higher in terms of technology and price). If you want to research that level of HD, there are many makes out there (probably chief among them Panasonic and their P2 format-see the HVX-200), but the main manufacturers-Sony, Canon, JVC, Panny, etc. all have their versions of full HD gear.