What do I need to know about brands, features, resistance and buying choices? I know nothing on this subject so just about anything is enlightening!
From what I've seen on cycling websites, you might be better to get a spinning bike than a traditional exercise bike. If you get a good one, they tend to be really adjustable so you can get a good fit out of them. Schwinn is a decent make. Another option would be to buy a real bike and then buy a turbo trainer to fit it to for indoor use. This is the way I have mine set up. This gives you the option of training indoors in winter and being able to go for a nice bike ride in summer! http://www.evanscycles.com/categories/training-exercise/turbo-trainers If you take this option and buy a mountain bike with knobbly tires then your best bet is to get a rim driven trainer as you won't have to bother about changing the tires. Normal turbo trainers don't work so well with knobbly tires. http://www.evanscycles.com/products/minoura/e-rda-80-trainer-ec016844
If you're going to buy something from Frodo's links I'd wait a couple of days until our affiliate link for Evans Cycles is set up