My 10 "must have" apps on my E90 (previously my E60) are as follows:
1. Mail for Exchange - this is always the very first application that I install because it restores my contacts, calendar, and tasks.
2. Truphone - mVoIP is the primary reason that I purchased my first E series phone (an E60) and is still a one of my primary applications. While VoIP can be setup manually, the Truphone wizard makes it so easy that I can be making a VoIP call 5 minutes after reformatting my phone.
3. Y-Browser - I don't like the native S60 file browser.
4. Calcium - much better than the native S60 calculator and free.
5. Interactive Voice Call Master - I use my E90 extensively as a business phone and this application allows me to direct and filter calls. Friends and associates are put directly through whereas others are either directed to my business partner or voice mail.
6. QuickOffice - as I said, my E90 is primarily a business phone and I need to be able to read/revise Office documents on the fly.
7. S60 Tracker - I used to use Handy Taskman to replace the native S60 application but find that Tracker has more features.
8. Best Profiles - I need an application that auto changes my profile and Best Profiles is the best (and I have tested all the others).
9. SmartLight - I hate for the screen to dim when I'm reading something.
10. MobiReader - I always have several eBooks on my phone and this is the best reader available (and it's free).
i cant believe Conversation was on only one person's list. It is an immensely practical app to keep threads on individual sms history.
I had great hopes when this app came out (since I'm a big fan of GMail's threads and the iPhone SMS app, yes, shame on me =p), but it is UNusable. I have about 2000 SMS, and Conversation always gives me a 'Memory full' error. Then it is build into the Contacts app (which I don't really get), so to edit a contact, I had to wait for Conversation to finish loading or erroring out (about 2 minutes). I mean wtf, isn't it supposed to make readind SMSes faster and more convenient? A total fail. The idea is good though, once it has solved it's problems, it may become a good replacement for the horrible build-in message app.