It depends what you want to do with the garden after dark. Are you planning to spend time out there partying are do you just want an effect to view from the house? I think a movement-activated light on the back of the house is very useful, both for seeing where you're going and for security. Beyond that solar-powered lights look good are very cheap and only need occasional replacement batteries. Anything else would, I think, require a qualified electrician to lay cables, so why not ask their advice?