ThePete's 12 Second Japanese Lesson #3 Good Morning on 12seconds.tv
o ha i yo
You say this to people until around 11am. Then you switch to "こんにちわ" See 12sJ lesson #2 for more on "konnichiwa".
To learn more Japanese online, I recommend checking out Alex Brooke's LearnJapanesePod.com (also visit his site AlexBrooke.com to check out what else he's up to). You might also check out JapanesePod101.com or pick up the book Japanese from Zero: Volume 1 if you want to learn offline.
Did I get something wrong? Tell me! I've got a LOT to learn still, so please help me and others by commenting. Thanks!