Ok this is a tricky situation. Getting a good salary hike after resigning would be difficult. When did you resign ? if it was recently, than you don't need to mention that you have already resigned to the new company. When they ask you about your joining date, you can tell them that you can join in 15 minutes and they will be happy. (As most companies want candidates who join sooner) If you mention that you have already resigned, they will surely want to know why and you need to provide a good reason for that. Whether you have another offer on hand or not, is not very important here.
Did you resign because you were going to join another company, but now don't want to join the new company ?
Do let us know to understand the situation.