You can get Google Talk and Yahoo Messenger from here: BlackBerry - BlackBerry | Wireless Handheld Devices, Software & Services from Research In Motion (RIM)

You won't get that MSN Live Messenger to work from that page. I'm not sure if the AIM on that page works.

If you're interested in an all-in-one app, I recommend JiveTalk:
BeeJive :: JiveTalk mobile messenger - instant messaging to go
If you can afford JiveTalk, just get it. You won't be disappointed.

If you want to try some free ones, here are a couple: (I can't vouche for either of these, never used them)
WebMessenger Inc.
Palringo, description here: New BlackBerry IM service offers voice and picture sharing | BlackBerry Cool