i too had a Nokia 6300, its a great 'phone phone' but it lacks features.
I have a Blackberry 8800 from work and its shite! It constantly crashes, its not user friendly.
Also are you pals with your IT dept? You will need a subscription to blackberrys servers as they actually push the mail down to the handsets, your exchange server basically sends it to them (RIM) and they forward it to the handset. I personally think their handsets are shite, the new touch screen one is bloody awful!
I now have an old HTC TyTn, which has been updated to use Windows Mobile 6, i find it excellent, it syncs directly with exchange at work, syncs all my contacts appointments and e-mails, looks same as outlook, you can easily set which folders to download, and file size limits.
It syncs either over 3G / GPRS / Wifi, it also supports direct push, so the instant you get a mail its pushed to your work PC and WM6 device.
It has a slide out full qwerty keyboard, easy to use, fast, i have Skype on it msn, supports picture messages, it does everything. I am also running TomTom on it.
The later TyTn II's have GPS built in, the new daddy is the HTC Touch Pro, which has a 3D engine capable CPU, allows 'gesters' on the touch screen, flicking and so on.
I would strongly look at the HTC Touch Pro
