I am a mage, and while I don't usually use followers, I thought it would be cool to go around with one sometimes. I have not yet found a mage follower - though I haven't really looked because I have always been a warrior and never used followers. Are there any good ones?

Oh ya, there are a ton!
http://www.uesp.net/wiki/Skyrim:Followers

I liked the guy you get after doing his quest in the Dawnstar inn.

Which one is that one?

Bear in mind, mage companions in Skyrim still have a tendency to burn, freeze, and electrocute the people they accompany. If friendly fire is something that adds a thrill to your life, hesitate no further.

What does the "max level" mean in the follower stats? Is that how high their level goes up to? If so, and you get a follower at level 20, can they increase their level when you are say, level 50 if it says their level goes that high (like Farkas)?

the merc in riften

Theres Marcurio, the mercenary in the Bee and Barb, Riften. He's an excellent follower.
There's Erandur, in the Dawnstar inn. You'll need to do his quest though ...
There are three Mage apprentices (Brelyna, J'Zargo and Onmund) in the College of Winterhold, each with their own quests. Once you complete those quests, you can ask them to follow you.

There are also quite a few mage companions, from starter level to 30+, upon Skyrim Nexus. Just search in companions (other) under Advanced Search.

Your followers level with you. Even if you don't always use them, the next time you pick them up they'll automatically catch up, so to speak.

I have had three followers: Onmund from the College, Brelyna from the College, and Erandur from Dawnstar.

Onmund svcked because he didn't have sneak as a major skill, meaning he sniffed and coughed and bumped into me a lot. He also only knew one spell from what I could tell. Died many times and was worthless to me.

Erandur ^^

Brelyna has Sneak as a major skill. We are never detected. Usually she is detected running after an enemy I haven't even seen yet, serving as a great distraction while I persue the appointed path. She is equipped with a Flame Atronach, and an enchanted sword that I've not looked at. She also glows with a Ward or Flesh spell. I have abandoned her with four bears and she caught up to me. And her favors are dead easy to accomplish. I wouldn't trade her for any other mage.

This, though in my particular experience it was with Lydia as my follower and a mage dead thrall I had. At the end of just about every fight Lydia and my mage thrall would be going at it leaving Lydia taking a knee frequently. Guess she got tired of taking lightning bolts to the back but could never take the mage and her summons. Finally had to dispose of the thrall. I assume the follower AI isn't any different.

I haven't checked yet, but I know that in Oblivion there were PC-based mods allowing you to add and remove spells from your companions' list. I'd have no problem with a mage companion who only cast heals and summons. It's the stuff from the school of Destruction that leads me to think it was acquired in some cases from the correspondence school of Destruction.

Don't forget about Illia from darklight tower, she's a badass mage and the only one (who I have met) who will cast paralysis spell. Just take note to not dismiss her if your game is before 1.4 patch since you won't be able to recruit her again.

The Female Dunmer in the Mages College, and The Mage in the Riften Pub.. Thats all I remember.

Edit: Oh! And the Female Dunmer who tends to Azura's shrine. Jzaargo is also a good choice, because he knows the "Heal Other" spell.

There are mods such as UFO that will allow you to set the companions to ignore FF issues in combat. It's actually a simple setting that can be changed but they allow you to do it via character dialogue. Makes things like fractricide between multiple companions / Dead Thralls a thing of the past.

As for companions, I'd almost say to pass on Marcurio. Is he a bad mage/compaion? Oh no... no not at all. It's just that he's SOOO good that he'll almost be the main character in your place. NPC mages in general in this game can be really insane when leveled up with their near perfect aim with spells (it is perfect with instant hit shock spells), never loose track of targets, can see perfectly in any weather or light condition... etc. Typical AI targeting issues that you see in FPS games which this game basically is.

Seriously, you get him going and he can clean up just about any situation I've come across, and this is with all sorts of difficulty enhancers and extra spawn mods on Master. He is a spectacular companion and if you're struggling you should most certainly give him a tryout.

Marcurio is an excellent mage, follower

especially if you equip him with some enhcanted items, to raise his magic and lessen cost of destruction spell.

he will become a killer, and steal kills from you, which svcked as iwas going for my one hand and two handed perks.