The first parking place I can recomend is Macro office lot (opposite side of Sukhumvit rd.),but the time there is limited 9.00-21.00 (free,sometimes tip to the guard).The second is of course Emporium (you have to spend there at least 30 min. to find the place) and the third is gasoline station on soi 26 (30 baht,time unlimited).