I have Petstairz foam stairs that I bought about 8 or 9 years ago and they are just now starting to look crappy. They are foam and I have been pretty happy with them all this time. I have the 5-stairs up to my bed and they all use them all the time. They weren't cheap but they have lasted.
http://www.petstairz.com/
If you want wood ones, Peachbongi posted this thread a while ago about an item she bought on ebay and was very happy with.
http://www.yorkietalk.com/forums/yor...gie-steps.html