Depends what you want it for to be honest. If it's a business phone that you'll be using in your day-to-day role then you probably can't go wrong with any of the blackberry models (if they're available to you at a decent price).
If your work are just supplying you with a phone through their company scheme and you aren't using it for actual work tasks then you could probably go with the LG Viewty or Nokia N95. They're two of the more popular models on the market at the moment. The Viewty is basically LG's answer to the iPhone (although it's a bit more camera orientated) and has a number of impressive features, the N95 is of similar spec, but you can get it with a massive 8 gigs of memory which is great for storing music, movies, photos and games.
In response to King Carl's comments, I think the N95 software works well, I haven't heard of any existing issues (although that doesn't mean that they're aren't any), however I do know of a problem with the software on some of the newer Sony Ericsson models which can be fixed by updating your phone using the data cable provided with your handset.
I think I'm going to stop there, as I'm coming dangerously close to sounding like a Carphone Warehouse sales assistant. (No offence to any Carphone Warehouse sales assistants out there).