I disagree on Reaction, simply because Riggers with Rating 3 Control Rigs very rarely needs to roll more than 1 or 2 hits for nearly any vehicle test they're called upon to make (that is, unless you frequently drive sports cars on mountain roads covered in black ice in the dark during a snow storm pulling crazy stunts the whole way).
Piloting skills are to my mind important, as are the Electronic Warfare and Gunnery skills. Unfortunately, so many of the Matrix related skills are nearly useless to a Rigger because most of the Matrix Actions require Sleaze or Attack attributes, which means a Rigger can't perform them himself.
In terms of skills riggers are likely to use, you're looking at:
Gunnery (can be used with Logic if Sensor Targeting is used; this is NOT an optional rule, and should require absolutely no clearing with GM first)
Sneaking (used with Intuition according to the core book)
Perception (can and should, in my opinion, be substituted with the Electronic Warfare skill, still uses Intuition)
Pilot X (whatever you want to be prepared for)
Navigation (lets face it, no one else takes this unless they take the outdoors skill group, so as a Rigger you probably should be able to have a sense of direction
)
Electronic Warfare (used to both Compensate on the Fly and Perception)
Computer (used to spot the opponents that are hiding, highly useful on your own and as a secondary spotter when there's a matrix specialist around)
Skills like engineering, hardware, and software are handy, but not what I would consider essential.
Matrix Actions you're actually able to perform:
Change Icon (yay... seriously, buy a Wrapper program)
Control Device (various)
Disarm Data Bomb (Software)
Edit File (Computer)
Enter/Exit Host
Full Matrix Defense (no skill)
Grid Hop (no skill unless you hack...)
Invite Mark (no skill)
Jack Out (biggest reason to take Hardware)
Jump Into Rigged Device (only requires a test if you don't own the device, and you can't hack the required marks on the device, so not really sure when this would ever apply)
Matrix Perception (Computer, and biggest reason to take Computer to my mind)
Matrix Search (You might already have Computer, and a browse program adds some versatility to the teams matrix specialist in terms of more information browsing capabilities)
Reboot Device (Computer)
Send Message (no skill)
Switch Interface Mode (no skill)
Trace Icon (Computer, but requires 2 marks so you'll be unlikely to be able to use this unless the opponent is somewhat incompetent)
So, out of a grand total 30 actions, you get to use 16 of them, 8 of which has an associated skill. Make of that what you will.