Classic Charcoal Gray Suit - Stick with a perfectly tailored and trim fitting suit. Make sure it compliments you and actually fits. Go with a charcoal gray, it will go with anything. You should already know what suit I am describing; yes the "Money Suit". If you live in an area where the weather is appropriate, you might want to break out the flannel suit for this occasion, but remember there will be dancing. Trust me, there will be dancing.
Black Oxford Shoes - Wear the classic black oxford shoes. This is the perfect occasion to breakout the shoes that you wear to interviews, weddings and funerals. Now add Holiday Parties to that list.
Dress Shirt - Keep it classic. The well tailored, white dress shirt with medium spread pin point collar is the perfect call for the occasion. Think of it as the base for your tie and pocket square selection. It also makes the transition to the after party very well. Just undue the collar roll up the sleeves and you can hang all night without looking like you walked out of a Christmas themed nightmare. Remember, there will be lots of pictures and some sent to your clients and vendors, keep it classic.
Tie - For the tie I would recommend a classic gray tie with hints of red or maroon or burgundy. This will give it a hint of the holidays without making it look like you've been dreaming of a white Christmas since July. I also think a solid dark red tie in a satin or silk would look great. If you are going with a pattern, keep it small and classic. A wool tie or silk knit would also look great, as the fabric would play well against the worsted wool suit. As always make sure the tie is 3" or skinnier. Since it is a party, you can go with a tie skinnier than normal, but please do yourself a favor and do not go down to the 2" tie.
Pocket Square - Have some fun, it is a party after all. Go with a wool or silk red pocket square, patterned with other colors if it is wool. If it is silk, go with a dark red and avoid the true red. Another great option is the always appropriate white linen pocket square, worn off slightly off kilter.
Sprezzatura - Don't look too perfect. That is an easy way too look like a nancy and have everyone hate you. Mess something up a little bit. Unbutton your cuffs, mess up the tie a bit, keep the pocket square sloppy. No man should ever look perfect.
Socks - Have a lot of fun with your socks. Make them brightly colored, striped, paisley, or another pattern. Make them a different color than the suit and shirt. Wear red, green, whatever. This is a great opportunity to wear green and red plaid to go with the Christmas spirit, like the one above sold at Ben Silver. It will be recognized and you will lauded for having pride in the season.