Gravity, Profimail, Handy Profiles, and more
I don't think I have any of these on my E72.
But I do have others that I regard as essential; no idea if they're on the Ovi store, since you can of course buy Symbian apps from anywhere you like.
Profimail: a very good email client, with support for multiple POP3/IMAP accounts, full support for IMAP folders, message rules.
Gravity: Twitter client; apparently also supports Facebook for people who use that
Handy Profiles: An improved profile manager, which supports rules such as switching my phone to a 'private' profile overnight that means only family and some friends can wake me up, or other profiles based on calendar entries or even which cell I'm connected.
An honourable mention to Telexy's SymVPN too, which provides a PPTP VPN (couldn't get on with IPsec) and allows me to use the built in Nokia SIP client to connect to my home PBX from wherever I am.