Budget
Bansabai Hostel
This "hostel" is not really a hostel, more like a three-star hotel. It is unbelievably hard to find as it is deep in the sois of Lat Phrao, and about 16 kilometres from Victory Monument! So budget in some money for long taxi rides. The English skills of the staff are not that good, but no wonder, as this is far off in a quiet residential neighbourhood. At least they try all they can, and are very responsible and hospitable. You get a lot of service for your money: a huge room, that is very clean, a balcony, air-conditioning, pool, fridge, cable TV, room service and a cheap mini bar.
Chewhouse Guest House
An excellent guest house run by three friendly Thai pilots; one speaks fluent English from living in the United States for two years. There are ensuite rooms and dorm-type rooms. It has a great backpacker vibe and cheap beer, as well as free Wi-Fi, water, kitchen facilities and warm water showers.
Midrange
Amari Don Muang Airport
This four-star hotel is right beside Don Muang Airport and even connected to its terminal buildings by an enclosed overhead walkway. Since the opening of Suvarnabhumi Airport, the quality has gone down steadily though. While still a good hotel, breakfast, service and rooms are less impressive than before. Three restaurants closed down and there's only one left now, and breakfast is not included by default. There's still a good pool though.
Mystic Place
Far off the wackiest place to stay in northern Bangkok, Mystic Place is a super-kitschy hotel. Each of the guest rooms has been designed by a different interior designer. Expect a full dose of clashing colours, bright plastic furniture and colourful mood lighting. Note that Reflections moved in 2008, the new location is less convenient and no longer has a pool.
Rama Gardens
By any means a large and pleasant hotel. Rooms are spacious, comfortable and clean. Also has an elegant lobby, nice front gardens and a large breakfast. It is mostly useful if you're taking off from Don Muang Airport or maybe if you want to stay closer to Ko Kret.
Sofitel Centara Grand
It is really far from downtown, but at least close to a convention centre, shopping centre and easily accessed from the expressway and metro. It is probably the best dig in this part of town.