I LOVED Trixie Belden!!!! I was a devoted reader as a child, and these were my favorites. I liked Nancy Drew, too, but she was a little older than me and I couldn't really relate to her as well. Trixie and the other BWG, on the other hand, were my very dear friends. Several years ago the entire set was reprinted in paperback and I bought and reread numbers 1 - 38. On Ebay one day a few years ago, I found that the series ended with number 39. Believe me, I felt as though I had gotten a real bargain when I only had to pay $65.00 for it (a used paperback that originally cost $1.95!) Well worth it to have the whole set, which I reread every few years. Neither of my daughters, who are also great readers, have been very interested, although younger DD11 recently started the first one and said she liked it.
I loved all the other books that have been mentioned, especially the Shoe books and other by Noel Streatfield. The Magic Summer and The House at Caldicott Place were my very favorites. Also, the Elizabeth Enright books - The Saturdays, The Four-Story Mistake, etc. and Gone Away Lake and Return to Gone Away Lake. And yes, I have all these books upstairs and I may have to go read now!!!!!