For most purposes, they are every bit as good as the own brand ones, but they will probbly lack one or two features, which may or may not be of concern.
If you want to use them off camera then it doesn't matter what you get so long as it has a PC sync terminal or you can adapt the hot shoe to take a PC sync though too. I got a 2nd Nikon SB-24 for that purpose.
Add your wireless trigger of choice and hey presto. eBay triggers are pretty good for the money.
Then read this http://strobist.blogspot.com/2006/03/lighting-101.html
Using the flash off camera will open up more creative ideas too.
These were taken with two off camera flashes.
And here's my wireless flash set up.
Now the skater pic is quality...
...and here's mine
[url= http://farm4.static.flickr.com/3489/3194988756_e425a1da68_o.jp g" target="_blank">
I bought a Sigma EF-500 off Ebay a couple of years ago, and it was fine until until I dropped it. Dropped once, broke once at the plastic foot. Now I have a Canon 580EX-II as it has a metal foot, much more robust and a wee bit more expensive. The 430EX-II also comes with a metal foot but is out of the price range but is a bit cheaper than the 580. I also have a $35.00 slave flash, again from Ebay which is OK and works well with Canon cameras but only syncs to 1/200.
So for general use I'd go for something really cheap, the $35.00 is limited, but OK, the Sigma was a good flash but too fragile. The 580EX-II is the dog's danglies, but expensive.
What do you wantto use it for?
[url= http://www.bhphotovideo.com/c/shop/647/Camera_Flashes_Dedicated.html ]here[/url] might be worth a look, very trustworthy, I've bought several lenses from them.