You already had the best (Primer)
After that, in no particular order:
Sneakers. Brilliant film.
Hackers - I think it's old enough now to be allowed but it was really laughable at the time - in the kind of way swordfish will be almost respected 20 years from now.
Wargames is the Hackers of the early 80s.
Pirates of Silicon Valley is also worth a watch.
Three Days of the Condor is a fantastic film if you're even slightly old school.
The nines is one of those films you'll either get and love or won't - I loved it.
Battle Royale is an amazing film that happens to have some hacking in it.
2001 is the ultimate hacker film, even though there's not much that you could associate hacking with it. The way it's put together, the dedication to realism, the way the special effects were implemented a year before man went to the moon defines it as a hacker film for me, although YMMV.