You don't say where you are. If northeast/mid Atlantic, I like Viwinco for replacements. Been around for a long time, excellent service, warranty. For new construction windows, I like Andersen 400. There are other good ones, but not at big box stores.
Replacements are usually all a small home can afford, but new construction windows have benefits that replacements don't have. With either, proper installation is a must. Poorly done high performance windows are no better that 50 yr old windows.
Don't beleive that crap about "they'll pay for themselves, quickly". They will, but it will take a long time. Figure to save 20-30% on fuel savings over single glazed windows.
Last edited by Just Bill; 01-20-2010 at 07:44 AM.