In Prog 1322 Megacity One was invaded by some rather familliar looking xenomorphs in a rare 2000AD crossover. The tale, written by Wagner and Diggle featured sumptuous art by Henry Flint and some amazing covers. All of these are shown below:
Prog 1322 by Kev Walker:
Prog 1324 by Greg Staples:
Wraparound 1330 by Fraser Irving:
Two variant covers for the finale of the story in Prog 1335 by the wonderful Jock:
Another Hollywood alien that Dredd has trounced is Predator. Here are two of the four covers I know of, starting with Mr Bolland's Judge Pred:
And Duncan Fegredo:
There were also covers by Dermot Power and Martin Emond but as yet I cant find any sullied versions!