I've found that Arsenal and Runner's Companion are both books that every character build will want to at least contemplate. The rest are more specialized.
Sixth World Almanac is a good history run-down for those that want to see what's been going on in the 6
th World. (Over twenty years of RL and Game life do seem intimidating to a lot of folks.). Also good if you want to create a character that doesn't come from Seattle.
Attitude is a good book for a modern view of how things are in the world. Fluff for the most part, but good fluff. Honestly, the worst review of it I've heard was "It wasn't as good as one of the best books that came out in the old days.", which is a pretty bloody good review. (The crunch in the book, however, needed some more proofing. But as it's the major minority, that's not a big issue.).
Seattle 2072 is a great book if you want to base your game in the stereotypical Shadowrunner city of, well, Seattle.

Full of information on the city, politics, people, and places.

For the E-Books, I'd suggest choosing them based on what your group likes, but "This Old Drone" is a must-buy in my mind if your group does any kind of drone work at all. Gun Heaven is good as well, if you have any Gun Nuts in the group. (Not you,
The Gun Nut.), and might want a classic piece of gunmetal. I know I wouldn't mind a 150
th Anniversary Colt M1911 as a nice example.

(It isn't in Gun Heaven, but the Colt M1991 is, which is an ergonomically redesigned M1911, so is close enough.).
And, to make Bull happy (And because they're good suggestions), the Shadowrun Mission adventures.
