The answer to your needs is a wonderful 4E DM trick called 'reskinning.' Because there's no real 'template' for what an undead monster is, stat wise, you just grab a monster you like, and you reskin it.
For instance, the Hungry Dire Wolf is a level 4 skirmisher. Rename it 'undead wolf,' and describe it as missing most of the flesh from its body and tell the players they can see its rib cage, and bam, an undead monster that is very different from the standard fare.
For a more intricate one, the Grell Strangler, as a skirmisher, has the theme of grabbing things and dragging them away. With reflavoring, this can easily be a type of undead that grabs the PCs and drags them away to be eaten (BRAAAINNNSSS). Just change the name of the abilities, change the tentacle lash damage from poison to physical, and flavor the ongoing damage from the grab as 'being chewed on' and you have a creature that will scare the snot out of your PCs.
Basically, don't consider yourself constrained to only using undead stat blocks that are actually undead. Use any appropriate on-level monster that would make an interesting encounter, and call it undead.
/secret DM trick