UFC 125 will be carried live on pay-per-view with three preliminary fights airing on the ION network.
If you lack access to the PPV feed for whatever reason you can always go the live streaming route and view the fight card on your computer.
There is really only one way to get a legal live stream and that is from the UFC themselves. So, avoid the nefarious "live streaming" sites and head on over to http://www.ufc.com/event/UFC125/watch#online and see which option suits your needs.
The UFC.com deal is $44.99 or $74.98 if you would like access to the fight as well as the UFC vault streams.