At my work I have a Lotus Notes account, but not the Lotus Notes client, so I must have the browser open all the time, just to be notified of e-mail or calendar events. As I don't like having it open (it eats resurces) and it's annoying to click on a dialog each time the browser session is about to expire, I use some useful utilities.
For the e-mail events, I have POP Peeper. It is a small application that notifies you when new e-mails arrive. It can handle more than one account and you can choose the kind of alert signal you prefer: a flag in the system tray, a dialog, etc.
For the calendar events, I use Personal Reminder. It's a very simple application that allows you to insert entries to remind, when you want to be reminded and the repetition of notification if you need it (to remind you every day, every week, etc.).
I love these kind of small apps: simple to install, small size, simple and intuitive to use, ...