I believe the Corsair vx series (450-550w) are made by CWT and the hx series (520-620w) ones are made by Seasonic. I don't think either one of them makes a bad PSU. Yes they farm out to whatever PSU manufacturer that meets their guidelines, but with a 5 yr. warranty, it helps. I'm not saying that the 5 yr. warranty seals the deal, but it should be considered when purchasing a PSU. I know the Ultra PSU's have a limited lifetime warranty, but you won't get me to buy one right now. This is just a personal preference and not any reflection of the company. I've just read too many posts that have had issues with at least the older Ultra's, so I tend to stay away. This also doesn't mean that other "quality" PSU comapnies have had or still have iffy designs, but this is just something to consider. If you do your research on your parts, you will feel better about your decisions and hopefully will have quality parts that don't go south on you.
As far as getting PSU's online and paying shipping/taxes, most of the time I look for a PSU locally, they either don't have what I want or it is too expensive. So I tend to buy my parts online, since they usually have what I need and have it for quite a bit less than a local shop. To each his own. Hopefully that helps you in your decision.