You can view these attachments through just BWC:
DOC, TXT, XLS, PDF
Perhaps one or two other formats, not sure which ones. No embedded images without BES, no fancy formatting without BES.
Verichat will work without BES on Cingular, it just takes a little bit of hoop-jumping with the Cingular representatives to enable the Internet features on the BlackBerry.
HTML browsing will definitely work on Cingular, and even if the BlackBerry browser is not enabled, you can get Reqwireless WebViewer 4.0 at http://www.reqwireless.com
(get the corporate BlackBerry version)
You sound like a user who can probably get by without BES. Just be prepared for a little bit of hoop-jumping on the phone with Cingular in the first week or two. You can always get BES later for $10 to $25 per month (see Hosted BES FAQ