Firewall / IDS for web db app site

[jp () sociustechnologies com]

Hi all,

I'm building a .com project (web db style with e-commerce parts, looks like ColdFusion might be the tool we'll use) and 
I'm working on the architecture.

For the firewall / IDS part, I need advice.  

I'm thinking either Cisco 506 or m0n0wall to protect the db server.  What about IDS - do I need it?  Snort a good 
choice?

Thanks!