Working on a little secret project (well, one I can't mention yet on the blog) I've been trying some of the laser-cut card windows from Truetexture.
Each one is made up of 4 parts nicely cut in card less than 1mm thick. The frames are lovely and fine and the extra thickness makes them look, to my eye, better than etched versions.
Assembly is simple enough using PVA glue and taking your time. Put the first one together without glue to get your head around the order the layers are placed in though.
The killer is probably the price. £4 for 4 windows isn't cheap. A Wills pack of plastic ones worked out a lot less money.
The advantage of these is that you get a lot more variety in styles but I think I'll keep them for foreground models only for the moment.