VLC
This page describe things what you can or cannot do with VLC.
VLC is easy to install on Windows (r), OS X or GNU/Linux. run the same way and do same things on all those platform.
Another interesting thing in VLC is the plugins architecture and the AJAX web interface.
Plugins can be used for example for digital zoom, transcoding, mosaic with 4,6,9,16,... cameras, realtime processing, ...
Now the last stable VLC compiled with the last version of Live555 can play up to 5 MPix resolution video. I also successfully recorded transcoded to mpeg4 video and viewed the result in the same time. It work on my notebook. (thinkpad T60 Intel Core2 2GHz, 2 GB RAM)
so the first basic thing you can do with VLC is to play both unicast or multicast stream from the camera.
just lunch:
vlc rtsp://192.168.0.9:554
Replace 192.168.0.9 with the IP address of your camera.
If you would like to try a precompiled version i did a .deb package for Ubuntu Gutsy, you can find info here ElphelSoftwareKit#Next_step:_ElphelLive_DVD_.26_Ubuntu_Gutsy_packages.
For other versions of VLC visit their page here http://www.videolan.org/vlc/
I will later add more tips on VLC here. Please fill free also to add interesting things.