For many years, I have always had very good luck at the independent 4*+ Siam City Hotel on Sri Ayutthaya Road. It has a nice bonus of being able to walk 5-ish minutes to the Phya Thai station, City Line, and head directly to the airport on the rail link. No taxi's needed, and for the solo traveler, much cheaper. ^ I was able to get the Siam City in February for about Baht 2500 excl breakfast. Easy to get to nightlife and shopping areas and back in the evening, too.

For a cheaper and simpler but highly respectable place, I like the St. James on Suk Soi 26, very near Emporium and the Phrom Phong Skytrain.