I figure the number, title and a short summary all help in order to know what book is being talked about. Here's my reference list for that. I'm only to #26 The Attack in my reread; I'll update this as I get farther.
# Title Description
0 The Andalite Chronicles Elfangor's pre-series travels
1 The Invasion Series intro
2 The Visitor Cat in Chapman's house
3 The Encounter Truck ship
4 The Message Find Ax under the ocean
5 The Predator Reveal that Eva is Visser One's host, other Marco family stuff
6 The Capture Yeerk medical center, Jake temporarily infested
7 The Stranger Ellimist appears during Yeerk Pool raid
7.1 Megamorphs #1 The Andalite's Gift Veleek
8 The Alien Ax phone home, Visser Three feeding ground
9 The Secret Lumber company front organization
10 The Android Introduction of the Chee/Pemalites
11 The Forgotten Steal experimental Bug fighter, end up in rainforest
12 The Reaction Jeremy Jason McCole, Rachel allergic to crocodile morph
13 The Change Ellimist, free Hork-Bajir, hidden valley, Tobias can morph from hawk
14 The Unknown Horse track, old Andalite toilet at Area 51 knockoff
15 The Escape Visser One shark-Controller project, Leeran introduction
16 The Warning AOL knockoff, Visser Three's brother
17 The Underground Oatmeal
18 The Decision Leeran homeworld
18.1 Megamorphs #2 In the Time of Dinosaurs Alien races on Earth in the late Cretaceous
19 The Departure Cassie snaps, and meets Aftran 942/Karen
20 The Discovery (David trilogy #1) Introduction of David and world leader summit
21 The Threat (David trilogy #2) David is a problem, Cousin Saddler injured, attempts to raid summit resort
22 The Solution (David trilogy #3) David defeated, summit sabotaged
22.1 The Hork-Bajir Chronicles Yeerk conquest of Hork-Bajir homeworld and Andalite involvement
23 The Pretender Tobias' father's will, apparent relative, free Hork-Bajir raid on Yeerk facility
24 The Suspicion Helmacrons
25 The Extreme Arctic, Venber
26 The Attack Ellimist-Crayak, Iskoort world, Animorphs+Erek vs. Howlers
27 The Exposed Chee malfunction, ultra deep sea mission to Pemalite ship
28 The Experiment Animal testing with chimpanzees, cow slaughterhouse
29 The Sickness YPM, Cassie morphs Yeerk, Ax deadly sick, others with flu
29.1 Megamorphs #3 Elfangor's Secret Visser Four Time Matrix alternate history
(The numbers for the companion books are to put them in chronological order)
