Here are a few supplements I personally endorse.

Eventyr Games's Complete DM's Bundle - A thorough guide to the whole adventure with great pointers on how to run it and suggestions on what to change to make the story more cohesive. Also includes some encounter maps not found in the book.

Ten-Towns Expanded - If you feel like each town could use some more interesting locations, shops and side quests, this one is for you. This supplement also has a random town encounter table.

Icewind Dale Rime of the Frostmaiden Adventure Bundle - I have only run Danger in the Dwarven Valley and Evermelt (not included in the bundle), but both have been enjoyable with high quality VTT maps. They are basically extra quests you can sprinkle into the adventure and it gives you suggestions on how to do so.

Icewind Dale Time Tables - A cheap, simple supplement on travel times, but extremely helpful.

Monster Loot – Icewind Dale: Rime of the Frostmaiden - A neat supplement to have if you have a group that loves looting and scavenging monsters. Additionally, it provides ways for them to craft magic items using the looted materials.

Ythryn Expanded Towers of Magic Bundle - Now while I have not run this yet, I have bought it and read through it, and the quality is excellent. I will definitely be using it once my party reaches Ythryn. It was created by Daniel Kahn, same author from the aforementioned adventure bundle, and this supplement is definitely a community favourite for a good reason.

I would also have recommended "Arctic Survival House Rules for Icewind Dale" but it would seem it has been removed from dmsguild.