After trying most of the calendar & PIM apps out there, I ALWAYS come back to the Calendar app that CAME with the iPhone. It's the best & most reliable.
After purchasing & installing multiple apps to keep track of our daily schedules, I keep coming back to the original Calendar app that came with the iPhone. All the others that I've tried, regardless of the price (some of them were pretty expensive), always had "issues". Some didn't do recurring events & didn't bother stating that in the description (mandatory for me), some didn't have any form of an alarm or only ONE alarm, & others would just flat out crash on a regular basis even after rebooting the phone after installation. I found tht the cooler they looked or the more expensive they were, the more disappointed I was after trying it. The original Calendar app not only does recurring events, but it also has multiple alarms for events. It's easy to use, easy to see ... just plain EASY. I love it! My only hope is that when they update the app, they add the option of recurring events M-F (weekdays) only. Right now the only way to have a M-F recurring event is to either set it to daily which will have it showing up on weekends too, or to create the event 5 times, once for each day of the week. It doesn't do imbedded pictures, maps, or any of that other stuff that some of the fancier ones in the App Store can do, but what it does do, it does very well & for that reason is the only calendar app on my phone. Reliability is everything when it comes to my schedule. If you're looking for a reliable PIM, I strongly suggest that you stick with the Calendar app at least for now. I'm sure eventually there will be another that works just as well, but as of now I haven't found one. I'm still waiting & hoping that DayTimer or DayRunner comes out with one for the iPhone. :)