Free Starter Version -
Free Accounting Software - QuickBooks - Overview
allows up to 20 customers ... allows you to add logos to your invoices ... not the greatest thing ever but cheap and cheerful
Apart from that you'll want your business cards (I've not used them but vistaprint.ie might be another cheap and cheerful option)
Maybe have a dedicated "work" mobile number as well (though having two mobiles eventually gets to be extremely annoying) At least with it though you can separate work / social life and advertise the work number on your site.