What is it max level?

Technically there is no level cap, but of course you can only raise a Skill to 100, which then limits your character to about level 75-80.
(assuming your Major Skills started around 30, and your Minor Skills started around 15.)

There are some in-game tricks to get higher, like going to Jail so that your Skills decrease, and therefore giving you the chance to increase them again.

There are quite a few mods that allow a different type of leveling, which can remove any limits to your Skills and Level.
Most notably is http://planetelderscrolls.gamespy.com/View.php?view=mods.detail&id=2030

I have it on good authority that it's possible to reach a level over 9000.

But seriously, the max level depends on your race/class setup. It's gonna be different for an Imperial Knight or a Bosmer Archer, etc. Also, it's possibe to exploit the game to break the limit and keep going higher, but it's hardly necessary. Characters over level 20 can easily beat the original game, and characters between 30 and 40 shouldn't have much trouble with expansions.

65,535 if I remember correctly. Even then I think it just overflows and hits 0 again.

There are different ways to answer this.

In game, no exploits, you will get to about Level 77 by maxing out all your Major Skills

If you do the Jail House trick, then you get to whatever level you want.

The question remains, why do you need to achieve the max level, there are no level related perks, once you get above about level 25 or so, in fact most of the level related goodies are given out before you reach level 20. There are no new critters at higher levels and your enemies do not scale with you in this game.

As for the game, Level 20 to 25 is all you need to beat the Main Quest, level 25 to 35 for Tribunal and Level 35 to 50 for Bloodmoon. Playing the game normally, you will reach these levels as you go through the game, even if you are not paying attention to Leveling.

I've got a character at level 75. Everything's maxed but Conjuration and Security, because I'm not a member of the proper clubs.

Books still cause character leveling, although my scores don't actually raise past 100. I thought that was a little weird.

I may have lost a couple levels along the way by failing to pay closer attention to skill raises.

I can remember playing vanilla Morrowind just for the levels and to max out attributes till there was only luck leftover at level time. Since it was fun just to level I did not mind that I was unstoppable.

Then I got GCD and MCA. I was like did that guy just kill me? ...me?

Now I don't notice the levels but the attribs, I still die even with like 160 wil and 180 int. I have a lot of mods and game changes, though I don't think I am much higher in the levels because of GCD post 60 slow down.

If u use the soultrap glitch to make any of your attributes like intelligence over 100, then u can train the skill to higher than 100. Take security for instance. Train with Hecerinde till your security is 100. Then keep training. Your security will never go above 100, but after every 10 trains you will still get a level up. Its much faster than the jail glitch. I got to level 114 till i got bored of it, but you could go much higher

Or you can just cast "Drain (skill) 100 on self for 2 seconds" and then get training from anyone, so it's only one gold piece.