Previously I had struggled to recommend a full system like Xero, or Quickbooks as it just resulted in more questions than progress. Quickbooks and Xero have now created products to bridge that gap though.
Quickbooks has come out with "Quickbooks Self Employed" quickbooks.intuit.com/self-employed/ which is amazing. It provides just enough bookkeeping functions, tax estimators and mileage trackers. All for about $5/month (if you send me a message I can get that price for you if you can't find it).
I test drove it this week and definitely recommend it to anyone that is a contractor, or sub contractor working for themselves. It will make your life at tax filing time infinitely easier, whether you file yourself or get us to do it.