I have made desk calendars for several years through Vistaprint and I get rave reviews for them. They're small, sturdy and inexpensive, and easy to read. About this time of year, I start getting queries from colleagues, friends and family who are all asking "Please tell me that I'm still on your desk calendar list for next year."
As a calendar maker, I find the Vistaprint interface very easy to use. I use a simple white template (see link below), upload one image for each month, plus one for the cover and I'm done. The space beside the monthly calendar accommodates images of various aspect ratios - by constrast, I've found that some calendar vendors require an image with a particular aspect ratio - and my best photos don't always fit that framework. Print quality is quite good (not awesome) but good, on thick, glossy stock. You can customize the holidays that appear on the calendar (I delete all of them).
A few times I've had quality control issues but I've always been able to speak to a live human being quickly and resolve the problem quickly, and Vistaprint expedites shipment of the reprinted calendars.
I only have a couple of quibbles: 1) The back side of the December page (never visible, but I know it's there) has info about the order (e.g., print date, a bar code etc) - unsightly but I don't know how to get rid of it; 2) there's no space (e.g., on a back page or extra page) to include additional information (e.g., my website, info about the animal rescue group whose images are featured in the calendar, etc). I can add a little information to the title (e.g., Catskill Animal Sanctuary 2016") but that's it. They also charge quite high fees for expedited shipping (but in my case, regular shipping gets the calendars to me in NYC pretty quickly).
I usually do a small test run of a few different designs (e.g., ordering 5 copies of 3-4 designs) to see how the calendars turn out, and if they turn out well, then I do a larger order. It's easy to edit a prior file (e.g., to replace images if I think I need to tweak the processing). There is good pricing for multiples once you order 5 or more and, currently, they've got good sales happening. Right now, I can order 10 desk calendars for $2.20 each plus "fairly flat-rate" shipping. (The multiples pricing jumps from 10 to 50, but I think you can order something in-between by dealing with them by phone.)
I have a Pro Advantage account (which I think I got for free) and that means the products don't have a Vistaprint logo on them, and I get free 7-day shipping on $150+ orders.
This is the design I use:
http://www.vistaprint.com/studio/calendar-design.aspx?template=55233_315&ag=...=image_41&rd=1