A nice metal clad exterior door would be an excellent choice if you're thinking about investing in new units and replacing your old ones. There are many different models available to choose between in simple as well as more elaborate designs which feature clad metal construction, sometimes in steel and sometimes in aluminum. Wood as well as vinyl are also common components in these doors for exterior use. Lowes and Home Depot are definitely worth a visit if you're on a budget, however you would like to get durable models that look good as well. Here are a couple of nice metal front doors:
ReliaBilt 36"W Oval Lite Steel Entry Door Unit Right Hand
"Compression weatherstripping for a tight seal. Ready for lockset and deadbolt. Ready-to-install door with frame. Limited Lifetime warranty."
Benchmark by Therma-Tru 36"W 9-Lite Exterior Grille Smooth Fiberglass Door Right Hand
"Won't warp, split, dent or rust. Simple style of a smooth surface. Ready-to-install door with frame. Limited lifetime warranty"
Can be found at lowes.com
Some of these doors would be suitable for an entrance as well as a back door. All of these units are very durable and feature quality construction that won't bend or warp because of the metal clad feature. Some of these doors feature a fiberglass window which is a really nice addition for decorative purposes as well as light entering your home. So if you're looking for the perfect exterior door for your home, them metal clad units are certainly a good choice.