Phoenix Audio Technologies has a USB based conference speakerphone called the Quattro3 which covers medium to large size conference rooms and has echo cancellation built into the unit. The Quattro3 also daisy chains to provide more coverage and pickup in rooms with poor acoustics.
To add on to Ashley's comment, I have listed a couple more echo cancelling USB mic/speaker combos:
Phoenix Audio Quattro MT304 - The one Ashley listed
ClearOne Chat 170 - can be daisy chained for larger rooms
Jabra Speak 410 - for smaller / huddle room setups
- this is good for smaller makeshift conference rooms with a webcam setup on a LED display
- make sure to order the USB female to male extension cable if you're placing it in a conference room and want to bring the mic out to a table
Just received a demonstration unit for the Logitech cc3000e unit, which when it gets to production in a month or so will be around $1000. It is absolutely the right solution for BlueJeans conferences in medium conference rooms (up to 10 people) with LCD displays or projector systems. The video can zoom in to white boards or specific speakers, and the audio is effective and loud enough for that large of a room. It can really pick up all speaker in the room. If you wish this to be a portable system and take from room to room, I would recommend a tripod or a microphone stand to hold the High quality camera. It does come with a wall mount/tripod set up.
The key is that the video and the audio is really great quality with this system very close to those room systems costing $8-10,000 more. So far, we have had no complaints (NO ECHO!) with this system, and hope to use it more (and buy more). This is the perfect complement for high end video conferencing with Blue Jeans - Get more with less cost!
None of these devices are really suitable for large auditorium spaces. There are more expensive, custom installed devices that be used in those situations. (Multi ceiling microphones, etc.)
We also use the Phoenix Quattro 3's and love them
We have a developer working on making the CC3000 work in linux as it is currently viewed as a mouse.
the other thing we have experimented with is using an android tablet in kiosk mode running the bluejeans app - this works great for interview rooms.
Along the same vein as the Android tablet, we have now got the AOC device working ( with the help of the wonderful people at bluejeans)