Not only does Sprint offer the cheapest BB data plans around, but they offer discounts of up to 27% depending on who your employer is. My plan is the Everything Data 450 BlackBerry:

450 Anytime Minutes
Nationwide Long Distance
AMERICA - ROAMING
Unlimited Sms Text Messaging
Unlimited Picture Mail
Unlimited Data Usage
Sprint Navigation
Unlimited Sprint Data
Unlimited Blackberry Access
Unlimited Any Mobile, Anytime
Caller ID, Call Waiting, Three-way Calling,Voicemail

After my discount I pay $51/month. What really makes this plan work for me is Sprint's "Any Mobile Anytime" feature that makes calls to ANY mobile phone free and not held against your minutes. So my paltry 450 minutes per month suddenly seems like a lot more. The overwhelming majority of my calls are to other mobile phones, and I haven't even come close to maxing my call minutes.