For work we have Exchange and I have Entourage to sync with iCal. We also so use BaseCamp that outputs iCal feeds. And for personal stuff I use Google Calendar (as does the rest of the family). So to bring it all together in one place I use BusyCal (
http://www.busymac.com/).
This works great with all the above. I do all my entries in BusyCal just selecting the calendar i'm working with and everything shows up for others where it should. It also allows you do to some other cool stuff. For example I can take a Basecamp Project calendar and republish it to google cal. It works great with Omnifocus. It also allows me to see a very complete picture of my work and personal life to avoid over booking myself.
For notes I use DevonThinkPro office. I started using this app when it was still in Beta and still use it everyday today. The ability to copy a link to a project file and past it in Omnifocus makes it super fast to link to items. I store a lot of data in DevonThink. I have several databases setup mainly one for work and one for personal.