Multiple google email accounts. What are my options?

I have a personal domain managed through google apps, a school account managed through google apps, and two gmail accounts.

I don’t know too much about integration of accounts, so could some google savy person tell me what they would do to make their life easier?

Too be honest, I wouldn’t mind keeping them all separate, but I now use Chrome and google notifier (on mac) and it keeps opening different accounts depending on what I logged into last.

I guess what I would like to do is keep my inboxes separate, yet log in using only 1 account and be able to select which account I send an email from when I compose. Is this even possible, and if so, how?