Level drain

[Sarisa]

In addition to all of the above very good suggestions I have one more to add:

Kill things faster. Dead things don't give you negative levels.

It is not really an option on some content (Ghosts of Perdition...) but you get neg levels back now relatively quickly many things that give neg levels won't neg you if you can kill them fast enough. Beholders especially, on a monk you should be able to take them down very quickly (consider maldroit handwraps of bone breaking, if you can find them).

Oh, and grind tangleroot for Flesh Rendor Visors

Just adding on to this, use and abuse your stuns as a Monk. Stunning Fist, Stunning Blow if you took it, and Kukan-Do at level 18 if you are light all make a huge difference in controlling negative level spamming mobs. In addition, Paralyzing handwraps are great, especially against Beholders.

[Meat-Head]

Plenty have said get the DW goggles from TR.

I highly recommend the silver flame necklace too. It really does absorb a lot.

Lastly, kill casters first and fastly. Use your monkish speed to get some fists up in der grillz.

[Grenada]

At higher levels, consider making a greensteel item with deathblock on it (since it sucks to have to put on armor/robes to get deathblock).

I'm working on a set of goggles with this exact effect. (triple neg goggles, stocked with as many immunities as i could get on them).

[pseudomasochist]

If you have UMD, you can also use Greater Restoration scrolls (Guild Vendor sells them), but note that negative levels will temporarily reduce your skill points, making it harder to reach a high enough UMD to cast the scrolls.

That's why I tend to carry regular Restoration scrolls instead of Greater. One level per cast is slow but 32 UMD is lots easier to reach after losing several levels than 44.

[Rusty_Can]

At higher levels, consider making a greensteel item with deathblock on it

Deathblock will stop "instant death" effects, such as Destruction, Slay Living, Finger of Death, Vorpal weapons, but not Enervate and Energy Drain.