I've said it before and I'll say it again!! I'm a huge fan of a savory pastry as a vegetarian meal for a special occasion. This time of year I like a double crusted pie. Hearty enough for meat eaters, can be made ahead and re=warmed, and is just as good at room temperature, so if it sits out that's fine. I have quite a few recipes. I just made a roasted butternut & fennel pie for Christmas eve, but I haven't written that one down yet!!

But...
Here's one with fennel, black beans and pecans...
http://outoftheordinaryfood.com/2012/11/22/say-happy-thanksgiving-with-a-double-crusted-fennel-pecan-and-black-bean-pie/

Mushroom
http://outoftheordinaryfood.com/2011/11/02/deep-mushroom-pie/

or roasted mushrooms with white beans, spinach and sage
http://outoftheordinaryfood.com/2012/12/13/white-bean-spinach-and-roasted-mushroom-pie-with-pecan-sage-crust/

Or chard, pistachios and golden raisins
http://outoftheordinaryfood.com/2011/10/21/chard-pistachio-golden-raisin-tart/

Or a chickpea pot pie...
http://outoftheordinaryfood.com/2012/11/20/chickpea-pot-pie-sweet-potato-hashbrowns/

I've got lots of others! It's what I really want to eat this time of year!

Emma.... The question asked for a entrée, not a main!

My suggestion would be do some devilled eggs.... I did them as a starter for Christmas day and they were a great success.

Tans

Lentils salade with tapenade on toast or if you feel crafty, in mini-nems. For the lentil salade: all you need is cooked lentils/ dressing: honey and french moustard/ and chives and confited lemon. It's really good at room temperature and nothing in it can tourn bad. For the tapenade (black olive puree) you can buy it done or made it mixinx a big can of black olives with fresh thyme or another herb you like.
The final look? Here: http://www.elle.fr/Elle-a-Table/Recettes-de-cuisine/Lentilles-tapenade-et-citron-confit-551508
And if you want to spoil your meat eaters invitees, buy some duck ham you can lie at the side and they can add in their own plates without bothering the veggi lot. Happy New Year

I would definitely make a cold pasta or rice salad...there are some recipes on bitesforbabies.com that could work such as, pesto caprese quinoa sald, pesto and ricotta pasta salad, caramelized onion, raisin and lentil quinoa, Italian rice salad, salmon orzo dill salad, just to name a few...;-)

Um...an entree IS a main.

I suggest you visit 101ccokbooks.com where you'd find a lot of options for just this sort of thing. Heidi's recipes are always a hit and generally are quite healthy.

I think the OP meant main dish, but an entree means something different based on where you are. In the US it can mean the main course, but here in Italy it means first course, not the main.

My favorite make-ahead new years dish is beef bourguignon. Since you want a vegetarian dish I would suggest making it with mushrooms, you really dont miss the meat and it only gets better as it sits.

SF Chronicle just published some appropriate recipes: http://www.sfgate.com/recipes/article/Start-off-new-year-with-lucky-legumes-4139495.php

It's tough to think of something that stays delicious when cold but this recipe came to mind. Portobello mushrooms get filled with an edamame pesto and quinoa. It may look like an appetizer but I serve it for dinner all the time. My anti-vegetarian husband loves it.

http://hotspicyandskinny.com/2012/08/08/edamame-aioli-pesto-and-quinoa-in-a-portobello/

I love lasagna for something like this, and it's actually what they do in Italy-- they make it and let it sit on the counter so when you order it, it might not be more lukewarm. I like mushroom lasagna or a nice vegetable one like roasted carrot and butternut squash lasagna for both meateaters and non-meateaters. Stuffed mushrooms are also a great option, because they are just as good at room temperature and they are hefty enough to serve as a main dish.