Psst, Jack. I did mention the Runner's Companion. I think you've got a data loop running, might want to clear your cache and check for tracer programs messing up your reads. 
I'll buck the trend here and suggest that really all you need is the SR4A core rule book. You can run a perfectly fine campaign with it alone, and indeed I'd probably recommend sticking to it if you're just getting back into the swing of things to prevent information overload. Shadowrun is a complex system with a lot of moving parts and the supplements increase the complexity significantly.
For example, I'd personally be very leery of grabbing the Companion right off the bat. It has some really cool rules in it, but unless you have a pretty well developed degree of system mastery it can also break the system fairly quickly. It has some nice new qualities, and the return of the priority system is a godsend for creating NPC's but a lot of the fancier metahuman species are difficult to work with for one reason or another.
Likewise Unwired and Streetmagic are handy if you've got players who are interested in running those archtypes, but if you don't or if they are still relatively new to the system themselves then you'd be doing yourself (and them) a favor by just running things straight from the core book.
Augmentation is probably a bit more general purpose, and serves to help a wider variety of archtypes but even then the genetech and nanotech rules add a layer of complexity that isn't really 'needed'.
Arsenal is probably the most useful of the supplements, if for no other reason than the wider variety of equipment that becomes available. The weapon and vehicle mod rules can be added as needed.
Seattle 2072 is a handy book if you plan on running around the plex and I'd honestly suggest that it should be the second book you buy unless you plan on setting the campaign somewhere else of course. If you can track down the older books in the "Seattle" series they're pretty useful too.
6th world almanac is a nice book, though I'm not sure if the editing issues have been fixed in the actual print product since I only have the PDF copy. It's hardly what I'd call essential though unless you really want to run a globetrotting campaign.
