When your old grill falls into a heap of rust it is a good time to pick one up. However, if you are looking for the time of year that gas grills are typically on sale, September and October are great months to pick up a grill. Home centers and specialty shops do not want to keep this year's models into next year. You will see discounts of 10 - 30%. You will find last year's models discounted through December but by December your choices will be more limited.
September is right around the corner. Get ready for those sales.
Tip: Keep your eyes open for circulars from Lowe's and Home Depot.