I had a couple of nights at City Lodge Soi 9 on my way back from Ko Samui - just needed a conveniently located hotel at a reasonable price. Think I paid around £23 a night or so. This hotel is very "no-frills" compared to the others I've stayed at in Bangkok. However, I chose it as I was arriving very late at night and just needed somewhere near the sky train in an area I knew.
It is literally at the bottom of the steps from Nana station - so if you are traveling with luggage you don't have to worry about battling your way along Sukhumvit Road (although there are quite a few steps at Nana station to tackle).
The hotel room was a bit worn out and past it. But it seemed clean enough - the bed was very comfortable and pretty much I only needed the room for a decent night's sleep.
If I was staying in Bangkok for any length of time I would choose somewhere else. But as I was just using this room as a base for about 36 hours it was fine.
Other good point about this hotel is that it is only a couple of steps away from Check Inn 99 (bar/restaurant) which is well worth a visit if you're in Bangkok.