I don't like onSnap and Popular-Domains because they use
outdated DeletedDomains.com databases. DeletedDomains
illegally use Exody's lists to power their search.
It's cool as long as you're not looking for freshly expired domains,
and want to dig through the "virtual leftovers". Once in a while
you get really lucky and find something decent.
If anything, I'd get Popular-Domains, at least it doesn't
crash. onSnap looks like it was slapped together in
about 15 minutes, and is missing some key components so
I'd stay away from it.
The cool thing is, you can download a free trial of
any of these, so just visit their web site and see
if it's something you're looking for.
I always recommend Domain-Retriever simply because
I created it based on customer feedback and included
features which my clients requested and the other
programs were lacking.
DR also comes with free Expired/Expiring/On-Hold lists
which we license from Exody. Our lists are updated
every ten minutes via direct FTP.
I will have a demo version of DR in two days, so you'll
be able to compare all three side by side
Best of luck!
Luc L.