Neutral:
* Relaxed
* Unmotivated
* Indolent
* Lackadaisical
* Easygoing
* Leisurely
Negative:
* Procrastinator
* Sluggish
* Idler
* Loafer
* Shiftless
* Lackadaisical (can be both neutral and negative)
Humorous:
* Couch potato
* Deadbeat
* Lazybones
* Slowpoke
The best euphemism for "lazy" will depend on the specific context and your desired tone.