Your book's cover is the most important part, as it is the portal to your story.
If you are doing a hardcover book, I would recommend you avoid the cloth or leather covers that have a die-cut window to display a single photo. I much prefer image wrapped covers with great photos and a catchy title. Most of these books will also include the title printed on the spine. iPhoto includes a dust cover with the same image, and other sites will charge a bit extra for this. This type of book looks great in galleries on on your bookshelf or as coffee table books. I tend to use the standard landscape hardcover for most vacation and gift projects, while my dad prefers 8x10 portrait size or larger square books for his beautiful travelogues. Pricing for a 20 page 8x11 inch hardcover book starts at about $25.99.
Softcover books are great for children's books, thank you books or smaller vacation mementos. I like to use the iPhoto spiral bound softcover for cookbooks so they can lay flat in the kitchen. 20 page softcover books range from $3.99 for a 3.5 x 2.6 inch book, $9.99 for 8x6 inches and $19.99 for an 11 x 8.5 inch book at iPhoto, which is pretty much market pricing.
Household inventories and garden planting guides are also good in paperback - just make sure that you add enough room for handwritten notes.