Software can be worth the expense if you really use it and plan to buy a lot of drops,(some software uses proxy servers and the free proxy lists suck so you may also have to pay a proxy site an additional monthly fee), but be sure to check out your free options.
I use domaintools.com often because it will sort domains to your preferance and that part of the site is free.
As for the question on backorders - snapnames.com is the best in my opinion, but if it is a hot domain be prepared to pay some big bucks.