Bikeisland wants $17 for a surly lockring, Soma wants $16 for theirs, that's kind of stiff either way. Dura Ace are $9-12 and as good as it gets.
The only cogs that aren't good are ones that come on cheap bikes, you really can't go online or into a store and actually buy a junky stamped cog any more. I mean, I'm sure there are shops that have old crap in the drawer or whatever, but all of the current brands are fine. Shimano/Dura Ace, Surly, Rockwerks (same as Surly), EAI, Soma, Milwaukee, Phil ($$$), Miche (not what you want), I may have forgotten one. The only weird name I've seen out there is "Cobra," Ben's has them and they're kind of scary cheap ($12), I'd skip them unless someone knowledgeable on here has seen them.
If you want to save money, get a $20 Milwaukee cog and one of the $9 lock rings from Ben's. I'd skip their $5 econo lock ring, not exactly the place to try to save $4. Otherwise, go to a local shop and pay a little more, but they will probably install it for free.