I agree with many of the posts here, basically to sum up the best course of action.
If you even think of wanting to dive more than just a couple of times, buy a better reg, around the 500-700 range. In looking at a reg, go for good engineering, good construction, good warranty, good ergonomics, and good performance.
Basically this rules out oceanic. I do not know about genesis or IDI. The regs look like knock-offs of the g250 and mark15 first stages.
Anyway, some good regs are
1. Apeks TX100, TX50, ATX200
2. Atomic B1, Z1 (Titanium is a gimmic)
3. Scubapro G250 HP, D400
I do not recommend Mares because I do not like the fact that they up the cracking effort to compensate for the fact that there are no adjustments on the reg. You can probably get around this if you know how to service the reg, but that said the mares abyss is a good reg.
To furhter narrow the choices, you have to decide if you want knobs or not. All of the regulators above can be adjusted, the only difference is some require tools, some require a twist of the knob. You only really adjust a regulator once, and that is it. I have had adjustable regs that I adjusted once and dove for years from 30' to 120' and never messed with it once. If you feel more comfortable with the extra "feature", then go with
1. Atomic B1, Z1
2. ScubaPro G250
3. Apeks ATX200, TX100
To narrow from there, if you are going to do some severe ice diving, etc... get a sealed first stage, that limits you to the apeks. I have tried the 100 and the 200, and found the 200 to be a more comfortable, better breathing reg. If you are not ice diving, go with a piston first stage and the atomic b1. Basically the same guy who designed the g250 designed the atomic b1. It is an iteration on a very good design and is superior to the g250 in every respect.
If you don't care about knobs, you want the fire and forget no hassel regulator, go with the d400.
Personally, I dive a d400.
If you want a cheap reg that you just want to play with, get a mk2 r190. It is a solid reg for about $300 and is a good performer.