1. Swallows and Amazons, by Arthur Ransome (#94 on the Top 100 list)
2. The Invisible Island, by Dean Marshall
3. The Children of Green Knowe, by Lucy M Boston (#98)
4. The Lion, the Witch and the Wardrobe, by C S Lewis (#4)
5. From the Mixed Up Files of Mrs Basil E Frankweiler, by E L Konigsburg (#5)
6. Gone-Away Lake, by Elizabeth Enright (#63)
7. Operation Yes, by Sara Lewis Holmes
8. Time at the Top, by Edward Ormondroyd
9. The Time Garden, by Edward Eager
10. Henry Huggins, by Beverly Cleary (#66)
It was hard to narrow it down to just ten books. The last few to be trimmed included Five Children and It, by E Nesbit (#112); Trixie Belden and the Secret of the Mansion, by Julie Campbell; The Vanishing Shadow, by Margaret Sutton;, and The Duck-Footed Hound, by Jim Kjelgaard.
Update 1815 27 Apr 10: My count for the top 100:
Three (Swallows and Amazons, The Children of Green Knowe and Henry Huggins) were on my original top-ten list;
I'd read 57 (possibly 59) others;*
I've seen the film version of one I haven't read;
and I'd never heard of seven of them (The Miraculous Journey of Edward Tulane, The Thief, Love That Dog, My Father's Dragon, Stargirl, The True Confessions of Charlotte Doyle and The BFG).
* I've read three others (including one of the seven I'd never heard of) since they were listed in the poll, bringing my total up to 63, or possibly 65, of the 100 - just under two-thirds.