Hey, we have the same last name:)!
In the book Beyond Jennifer and Jason, Madison and Montana, there are a bunch of lists in which names are grouped together according to some common trait (like biblical names, or Western cowboy names, or names from Disney movies). I couldn't find any lists that had both Isabel/Isabelle and Caleb in them, but here are some of the names each one was grouped with:
New England names:
Isaiah, Noah, Tobias, Jeremiah, Everett
Aaron, Isaac, Jared, Elijah, Jonah, Samson (plus most of the names above)
Fitting In/Standing Out(names that are a little less popular but not too off the wall):
Adrian, Carson, Duncan, Holden, Julian, Leo, Lucas, Owen, Seth, Trevor
Century names(slightly old-fashioned names that are gaining popularity):
Abigail, Eliza, Emma, Grace, Julia, Lillian, Lucy, Lydia, Madeleine, Ruby, Sadie, Sophia, Stella, Violet
Audrey, Bianca, Cordelia, Helena, Juliet, Miranda, Ophelia, Rosalind, Viola
Alexandra, Chloe, Felicity, Gabrielle, Julianna, Katherine, Lily, Natalie, Phoebe, Rebecca
Adrienne, Alanna, Beatrice, Camille, Celeste, Daphne, Francine, Gillian, Jenna, Jessa, Justine, Kirsten, Lara, Lia, Lila, Mara, Nina,, Olivia, Simone, Talia, Victoria, Zara, Zoe
Anastasia, Angelina, Ariadne, Colette, Daria, Genevieve, Regina, Thea
Ariane, Bernadette, Cecile, Corinne, Dominique, Elodie, Fabienne, Germaine, Joelle, Josette, Lianne, Lisette, Lourdes, Mirabelle, Morgane, Nicolette, Rachelle, Sandrine, Sidonie, Sylvie, Tenille, Venise, Zenobie
Whew! I hope this helps a little. My husband and I were just talking about the same thing a few days ago--our nine-month old daughter is named Clio, and when the next one comes along I haven't a clue what he or she will be named--nothing seems to sound right with it. Well, good luck(and congrats:))!