Cold Cut Sandwiches for a crowd...

Great suggestions everyone, Thank you!

For condiments, I would suggest a couple of flavored mayos -- whether you start with homemade mayo or not. You could add pesto to one and Sriracha to another and have a couple of great options within minutes.

Here's a recipe for Ina Garten's sun-dried tomato dip. I happen to love this on poultry sandwiches -- whether roasted or grilled chicken or sliced turkey. http://www.foodnetwork.com/recipes/ina-garten/sun-dried-tomato-dip-recipe

And, in general, a couple of nice homemade dips set out with chips, pretzels and crudités would be perfect (putting aside the fact that they can be used as condiments on the sandwiches) and can be made ahead.

Agree with MMH's suggestion about selections from an olive bar. In addition to olives, I've seen other items at olive bars such as roasted red peppers, marinated mushrooms, etc. that up the "specialness" with ease.

Instead of making sandwiches ahead, why not make a couple of platters with meats, cheeses, lettuce, breads, and have your guests create their own? It might be more interesting for them and they could then choose the ingredients they like and skip those they don't. Bonus: Less work for you, too!

I think a crudités are nice with humus in several flavors. You can use whatever veggies are pretty and in season. I also think a variety of olives are nice. Go to the olive bar at your grocery store. There are really nice items and you only have to plate them!

If you're serving sliced turkey, have a look at my recipe for [chicken] sandwiches with mango condiment and lime mayonnaise: https://food52.com/recipes/30927-chicken-amba-mango-condiment-sandwiches-with-lime-mayonnaise

It's old school. But those little sliced rye bread loafs. They're perfect size for sampling a wide variety of things instead of building a large sandwich, or for people that don't want an entire sandwich.
Also...don't forget pita bread, and glutin free options. Maybe some lettuce leaf, endive, or radicchio for making wraps. A tazakisauce would be nice too.

Muffuletta's done on a couple baguettes are so good, feed a crowd and cut beautifully! Also... they need to be prepared ahead so that eliminates as stress the day of!

Thousand Island and Russian dressing are good on cold cuts and easy to make at home.
Known for use on Reubens, hamburgers, iceberg lettuce wedge, day-after-Thanksgiving turkey sandwiches.
Easy to make at home and much better than bottled versions. Also you can control the fixings that go in or stay out, according to family tastes.
Here are a couple classic recipes:
http://www.thekitchn.com/how-to-make-classic-thousand-island-dressing-230560
http://www.bonappetit.com/recipe/russian-dressing

Depending upon what cold cuts you are choosing, I recommend serving a couple of really good mustards - such as a stone-ground Dijon and/or Dusseldorf. Tapenade made with ripe olives https://food52.com/recipes/6478-tapenade is a great condiment either to add to a sandwich or as a side. Also sliced Vidalia (or other sweet) onions.

Recommend basil pesto as a condiment. My favorite sandwich combo is turkey breast, pepperjack, pepperoncini/banana peppers, lettuce, tomato, and a smear of basil pesto. So pepperoncini as a sandwich accompaniment is nice too.