Shelley - I went through the process about a month ago - 8x10 and 11x14 are common though some architecture photographers have larger book. it also depends on the target viewers. If you're into commercial work where you have to mail your book to magazines, art directors, etc 11x14 or smaller portfolios would be easier to ship.
Recommended number of images range something between 10-25. There are other image layout options in addition to the usual one-image-per-page.
I personally use 11x14 portfolio from Lost Luggage (
http://www.lost-luggage.com/) They're based in Seattle,WA - order usually takes 5-7 days
I've seen porfolios of pro fashion photographers in NYC - they use the generic black leather kind (see Scott post for links).
a good book on this subject is "Portfolios that Sell" by Selina Oppenheim. though written for commercial photographers I find it very useful.
good luck