Like the other referral - Hotel Intercontinental has a wonderful Sunday Brunch and it is a beautiful property. Marriott Quorum has an indoor/outdoor pool, a wonderful breakfast that can be sent by room service and a great weekend rate. There are things to do in Addison such as Comedy Corner, Dueling Pianos, and usually something going on with the city. The restaurants are wonderful and you can have a loud fun to a romantic evening. Most Marriotts offer weekend rates.
Hotel Zaza is pricey but an outstanding property. It is in uptown so you can take a trolley ride, they are quite enjoyable, there are restaurants galore, Hard Rock Cafe and fun nightlife in the area. Hotel Crescent Court is across street and absoutely wonderful. If you want downtown, look at The "W" or Adolphus. The "W" is new and though I have not been there it is highly rated, in the Victory area and at the West End, which encourages walking in downtown and taking trains, horse drawn buggies and much fun. You can also look at the Adolphus which is my favorite. It is an Old World feel with each room different and 2 magnificent restaurants plus a bar/grill. Again, you're near West End. There is so much live music in the area that staying outdoors is a blast and can be very romantic.
By the way, I am a professional event planner so this is why I am very familiar with the hotel industry in Dallas. If you have any questions, feel free to e-mail.
Good luck and enjoy.