Issue 2 (first Judge Dredd) will be worth a small fortune, assuming it is in VG+/NM condition.
Issue 30 - 1st Rico.
Issue 119 - first ABC Warriors
Issue 149 - 1st Judge Death.
Issue 150 - 1st Judge Anderson.
Issue 228 - 1st Rogue Trooper
Issue 330 - 1st Slaine
Those are the main ones that come to mind (I'd say 1st Sinister Dexter, but IIRC that was in the mid-90s, so probably pretty common and relatively low-value by now).
Also, any issues by people like Grant Morrison, Warren Ellis, etc will be worth holding on to, to see if you can get them signed at conventions - that will significantly add to their value.
Edited by darkmorgado at 23:55:20 23-07-2012
Edited by darkmorgado at 23:56:36 23-07-2012