If you are just now getting into hand planes I would reccomend two.
A number 4 jack plane and low angle block plane.
Lowes sells a Stanly Bailey low angle block plane for about 30 bucks. Its a great little plane to grab to learn the ins and out of planeing.
Older Stanley Bailey #4s can be found on ebay for around 40$, and they seem to be the best overall value in used planes. There is a wealth of information available on the web about Baileys, so you can kind of get a feel for what you are buying.
Lie Nielson, Footprint, Sweethearts, and other expensive planes are nice, but I wouldnt get an expensive one first. I would start with something more affordable.
Whatever you end up getting, they aren't worth a damn unless they are razor sharp, and the sole needs to be flat. I sharpen my planes on my Diasharp sharpening stones, and I flattent the soles of planes with my 6 inch belt sander and my sharpening stones.
And honestly, any inexpensive used plane you come across can be made usable with some simple cleaning, sharpening, and flattening. So, if you come across some an unfamiliar brand for a few bucks, don't discount it. Like just about any tool, you can tell by looking at it if its junk, usable, or high quality.
I would definitely avoid ones with plastic handles and warped soles.