Place potatoes in a large saucepan and cover with water. Bring to a boil. Reduce heat; cover and cook for 15-20 minutes or until tender. Drain. Let stand until cool enough to handle or refrigerate overnight. Peel and cube potatoes.
In a large bowl, toss the potatoes, onions and celery. In a small bowl, combine the sour cream, mayonnaise, parsley, vinegar, salt, pepper and celery seed. Pour over potato mixture; toss to coat. Sprinkle with blue cheese. Cover and refrigerate for several hours before serving.