I’m not looking for suggestions for myself, but rather for the freelancers and contractors I work with and who send me their invoices. I especially like it when I get an invoice that has a button in it allowing me to pay using PayPal or a credit card. It saves me the effort and inconvenience of cutting and mailing checks, plus by allowing me to pay with a credit card it helps me manage cash flow, which means I may pay faster than I would if I had to cut a check from my bank account. And believe it or not I do like to pay my contractors as fast as I can so that they’re happy to keep doing work for me.
Some of my vendors use the online billing that integrated with Quickbooks, but Quickbooks isn’t always the right solution for an individual contractor. I’ve also received invoices from Blinksale, and those work just fine for me. But if anyone out there has other recommendations I can pass on to my vendors/contractors/freelancers please post a response.