I've seen Jeremy Ellis's stuff before, definite talent.
Hadn't seen that beat-boxer before (there's a lot of them nowadays!) but he's got down pretty well. I personally have to give it up to dubfx, which is just one man with a mic and a loop machine: http://www.youtube.com/watch?v=UiInBOVHpO8
Also to contribute, here's beat-boxer Killa Kela backing particularly good freestyle from Supernat (pay attention to the part with the flag): http://www.youtube.com/watch?v=I53jUHPeeGw
Curios what type of hardware dubfx was using in that video.. The string type and bass sounds he made, were not simply his voice sampled/looped there is some heavy processing going on to make it sound like that. You can hear some heavy delay/reverb/compression and such.
Which is great takes beatboxing to another level.
Producing beat sounds with your mouth eventually reach a limit and these guys are taking them to the next level with the assistance of hardware.
The loop station is a Boss RC-50. There is also a (Roland?) effects station you see him depressing the expression pedal on to add delay and apply other effects.
One last beatboxer vid I'd like to mention is this Julia Dales one, she's beatboxing without a mic covering her mouth. Two observations:
1) She gets good bass even without the proximity effect of the microphone.
2) You can see exactly what she's doing with her mouth to make the sounds which is interesting, to say the least.