Researching sideways (as Toni McKeen calls it)--looking for all siblings in each generation and their spouses/in-laws and even extended family members--takes time but it can be very productive. It led me to finding 2d cousins I never knew about!
Here's what happened: my first-cousin once removed really loved her favorite aunt Anna, who married my grand-uncle Sam. I decided to research Anna's family and found that there was no surname message board devoted to her family's last name, so I got permission from Ancestry to start one. That was in June.
Just two weeks ago, I got a note on that surname board from Burt, who told me he's related to Anna's family. He and I exchanged e-mails, I sent him a photo of Sam and Anna, and lo and behold, he gave me the e-mail of my second cousin Gary. Gary and I exchanged e-mails and the next thing I know, Gary's sister Bonnie called me to say how much she enjoyed seeing the photo of Sam and Anna--her grandparents! Plus Bonnie has some family tree info she got from a favorite aunt.
It's wonderful to get acquainted with these long-lost cousins and hear their stories. And it's all because of researching sideways. Gotta do more of that! Thank you, Burt, for taking the time to answer my query. More genealogy adventures are ahead, I'm sure.