I have an Allpro weight vest that goes up to a max weight load of 40 pounds (in half-pound iron rod increments), and I really really love it. I'm up to about 30 pounds right now (and I use a barbell that's about 55-57.5 pounds as well), and it's great to just be able to add a half pound here or a pound there as I see fit. I don't have any trouble getting it on or off.
The Allpro brand is good; however, it is cut in an "A" shape, so especially if you're shorter and/or short-waisted (like I am), you can feel like you're wearing a blue-plastic-and-iron pup-tent. It can feel a bit blossomy. Also, it can really hold your core heat in, which is no small matter in warmer, humid temperatures.
Also, the heavier the weight load on the vest, the more pull you'll feel on your traps. This might be something to pay attention to, and build endurance for.
I got mine at a local SportMart (which has now been acquired by SportsAuthority). You can also get them online; however, I'd call around to your local fitness emporiums before going online because the shipping costs can be horrendous because of the weight of the shipment.
HTH -
A-Jock