A lot of business are using Quickbooks or Sage Peachtree.
They start with fairly basic packages, and move on up as needed.
Inventory is always nice to have.
Keeping track of customers and outstanding invoices is critical for tracking what needs to be collected.
It's also nice keeping customer information, because you will be hearing from them over the years, as repeat customers.
It's nice to be able to go back and see the prior work that was performed.
They can ask what I installed for them last, and I can quickly pull that information up.
I use that feature a lot.
Some of my customers have moved many times by know, they call me whenever they move.