The DK series has a nice, small book about clematis that is basic and has good pictures (http://search.barnesandnoble.com/booksearch/isbnInquiry.asp?z=y&EAN=9780789441539&itm=87)

Viticellas are good starter plants. They are clematis that are vigorous, disease resistant, fast growers and floriferous bloomers. Also easy would be type 3's, meaning ones you prune to the ground each spring. Examples include easy ones to find like:

Jackmanii
Comtesse du Bouchaud
Prince Charles
Ville de Lyon
Earnest Markham

I use the HelpMeFindClematis website. There are thousands of pictures of hundreds of clematis cultivars posted there. Use the site's search feature to browse through them alphabetically. One thing to keep in mind as you search is that Clematis often have more than one name, so when you find one you like, you may find it in your local nursery or mailorder under another name.

Another site to browse is the American Clematis Society website:
http://clematis.org/

You need to look for clematis that are suitable for your zone/climate. I like Michael's advice about types and his cultivar choices. I would add General Sikorski and Niobe to his list, although they are type 2's, and require a little different pruning. You can find climate information, pictures, pruning details, plant size, alias names, etc., at HMFClematis.

Best wishes

Here is a link that might be useful: HMFClematis

A very good book on Clematis: Success with Clematis, by Marigold Badcock. Publisher: Guild of Master Craftsman Publications, 2005, ISBN 1-86108-407-2