I'm just starting out with Arcanum, and want to have a character that knows a few spells without being heavily invested in magic as a career path. What I'm wondering is, which is the best spell trees for this?

I gather that many spells draw their power form the caster's magical aptitude score, but I can't find a list of which spells anywhere. For example, I gather that Teleport will work no matter your character's aptitude, but what about Disintegrate? Or Tempus Fugit?

I haven't tried any magical characters yet, but my understanding is that pretty much all spells are affected by magical aptitude. Any spells that do damage will do more damage with higher aptitude. Also, spells can fail completely if aptitude is particularly low (if you are tech-aligned, basically).

I'm not sure how this would affect a spell like Teleport... I guess that it would sometimes fail to cast if your aptitude is low, but when it succeeds it would simply work. This means you could waste a bunch of fatigue, and would have trouble using Teleport to escape a fight, but for travel it would probably still work.

Keep in mind that in order to get the higher-level spells you will need to get all the preceding ones in that college, and each time you do, you will increase your magical aptitude. So unless you're actively bumping your tech aptitude as well, you'll probably end up with decent magical aptitude by the time you get a spell like Teleport.

Anyone else know whether certain spells depend less on aptitude?

General consensus seems to be that damaging spells will scale with the caster's magical aptitude, Teleport works as long as you don't risk spell failure through having a positive technological aptitude, and Disintegrate simply works from and on anything/anybody.
Apparently the Conveyance and Temporal colleges are quite nice and fun with an unaligned gunslinger.
I'm not entirely certain of this, but in my experience the stat-boosting spells are very on or off, with no change to their efficacy according to aptitude by caster or recipient, only a chance of spell failure.
White Necromancy does respond to magical aptitude in the caster, as I recall, but is still useful even with a high spell failure rate and low efficacy, since HP doesn't come back as easily as fatigue.

An unaligned gunslinger is exactly what I'm aiming for, so Conveyance and Temporal sound good to me. Thanks for the info!

Having done all tech gunslingers in the past my most recent Half-Ogre mage is an eye opener.

I would suggest initially getting harm for easy leveling then pick up the first 3 summonings(Ogre).
Lets you summon (early on) very strong mobs to distract and waste while you can sit back and shoot. :/ Fairly Willpower heavy but

I don't have much issue summoning at +20Magic aptitude.
Side note Learning schematics adds to Tech.(herbology is killing my magic aptitude)