Am I correct that the Beagle works realtime and the Saleae.com not ?
You're correct.
The Total Phase Data Center, the GUI for the Beagles, is great to work with. I haven't used the I2C/SPI Beagle, but I have used the USB480 Beagle.
I've also used the Saleae Logic. It has very primitive triggering (read: almost none), but comes with a pile of protocol decoders, which makes it a more versatile choice if you don't know what else you're going to get into.
(edit: fix typos)