Personally, I weigh every day. First thing in the morning, I wake up, have a wee (!), and then get on the scales. As my bathroom floor is uneven in some places, I make sure the scale is on a flat place, and then move it around to a couple of other flat places to make sure I can replicate the reading.
I don't need to weigh every day, but I like to see the fluctuations, both up and down, in my body's weight. If I weighed weekly, and my weigh day just happened to be on a day where I had fluctuated up (e.g., through retaining a lot of water from having not drunk enough the previous day), I'd feel quite disheartened because I'd feel as though I weighed something that may have actually been a distortion of my true progress. I weigh daily so these small changes up and down don't bother me at all. I used to get stressed by the scale not moving or going up, but I've relaxed about it a lot now (e.g., I
know I can't put on a pound of fat overnight!), and I now find it interesting and informative to see daily patterns.
I have a plain, inexpensive Salter glass digital scale. It is perfectly decent, and whilst it may not be the most amazing quality and have loads of bells and whistles, it was cheap and works perfectly well (i.e. reads reliably). If it broke, I'd definitely replace it with the same one.
http://www.amazon.co.uk/Salter-9048-...027344&sr=8-27