A consistent grievance of directory operators is dealing with automated or otherwise low quality submissions. Therefore I'd look for apps that provide strong options for blocking, filtering submissions by rules, bulk delete, automated sorting, etc.

Other features that matter:

• Good record of support
  
• Sophistication of admin panel: # options, granularity, ability to automate routine processes
  
• Clean, easy to modify templates
  
• Search engine friendly URLs
  
• Breadcrumb trail navigation as element of site nav
  
• Multiple admin options for handling listings: Featured, rotating, sorting
  
• Integration with payment processing if you plan paid listings
  
• ?
  

Thanks, webwork! I found vast numbers of offers, both free and commercial ones - is there a reason why I should go for the commercial ones other than service and support?

It's been my observation that the commercial ones tend to be a bit more robust. For example, better admin panels/controls, more options, etc.

It's a bit of a PITA doing a side by side. Where I'm headed is, in fact, doing a live side by side of several products.

Only because I love pain as I can think of no other reason for going through this experience . . . except to keep my eyes open for new developments, who is improving what and how, . .

I guess I'm prepared to argue for the idea that it makes sense to play with perhaps 2-4 flavors to truly guage what works best for any one of us. The cost is relatively cheap, at least compared to the value one may place on their time, and if any one version of script proves to save an extra hour or two in a month that script just might end up paying for itself in the first month or two - compared to the clunkier "free" or cheaper script.

My read suggests that the largest cost of any directory script is the time spent customizing it, updating it, etc. So, I'm inclined to not focus too much on cost - at least for the first few installations. ;)