There are three I can recommend:
Blue Elephant near the Silom BTS station:
Blue Elephant Bangkok Restaurant and Cooking School. Great food at very reasonable prices (4-700 baht per person), plus beverages at slightly inflated prices. Reservation recommended.
The Dome / Sirocco restaurants:
The Dome Bangkok. An outdoor/indoor restaurant on the 66th floor of the State Tower in Silom. A view to die for and good food, but expensive (1k+ per person), plus beverages at equally high prices. There is also an outdoor bar there. If you go for the view have a few drinks there before or after a dinner else where. Keep in mind that this place has dress code. I have seen people in jeans, though not technically allowed. Shorts
. If you go here I'll recommend making a reservation days before.
The third I don't know the name or the street, but I have attached a map. From Holiday Inn go down the road perpendicular to Silom rd. It is on the 1st or second road to the left about 100 meters down (total walking distance from HI ~300 meters). You can see their American Express Accepted sign from the corner. Great local restaurant with awesome food at low prices. Beverages other than wine are at on par prices, but you'll pay through the roof for wine (2k+ bath bottle).
Down near the river there are a bunch more. The three above give you a goo variety from simi up-scale Thai at fair prices to the cosmopolitan Thai at high prices to fantastic back-street Thai with great atmosphere.