The Hyatt Galleria (long stay apartments attached to the Hyatt Regency Hotel, near the mouth of the Creek in Deira) gives great unobstructed views of aircraft from the roof residents' pool deck (31st floor). If you booked into the hotel and asked nicely, I'm sure they'd give you access.
If the wind is from the north or west (which it is a lot of the time), take-offs from DXB go past the hotel at roughly the same height as the roof deck and I guess approx. 1km horizontal.