Disclaimer: I work for LifeSize Communications, so I might be biased...
Anyway, in the dedicated hardware area, you've got HP and Cisco at the high end (100k++++), Polycom and Tandberg (merging with Cisco) in the middle end (10k++) and LifeSize and a host of other smaller players at the low end (<20k). If you want HD (720p30 minimum), you're not really going to find it on PC based implementations, most are limited to 640x480p15 - 30 due to the compute required to encode the stream efficiently. Polycom and Tandberg offer a mix of SD and HD products with the SD products generally being cheaper than the HD ones. Everyone in the "professional" video conferencing space is moving to HD. LifeSize offers products from 2.5k (passport - 720p30 only, point to point only) to about 17k (room 220, 1080p30/720p60, 8 way multipoint, H.323) with a variety of products in between. We pride ourselves on needing the least bandwidth to achieve certain levels of performance (e.g., we'll do 720p30 in 768kbps, 720p60 in 1mbps and 1080p30 in < 2mbps). Polycom and Tandberg offerings are generally 2x the bandwidth at the same resolution/frame rate. Cisco's telepresence stuff needs (I could be wrong here, but I think I'm in the right ball park) something like 18mbps for the 3 screen solution you've seen on 24 and a couple of other shows (that's 6mbps/screen).
There are plenty of pc clients, but truth be told, they look like a** compared to the (HD) professional ones in my opinion. Of course, I'm starting to realize that HD TV looks like crap too, so it might just be me.