As a trust-worthy, less-expensive alternative (Bajo, no offense) who also speaks good English:
http://www.celano.com.ar
He did my residency (as well as 7 others I know personally) and just completed a friend's citizenship.
My friend was here for about a year and a half before he started the citizenship process, no residency, no visa. Celano's had quite a bit of citizenship business in the last few months, the only issue may be he's too busy to take on new clients (I don't know this, though I know he had a run a few months ago when everyone started worrying about being here irregularly).
He takes a portion up front (it was half for residency, I believe it's the same for citizenship) and the rest when the process is complete. But ask him for his terms
Steve is correct about not needing a lawyer for residency, though paying someone to help, who knows the process, wouldn't be a bad idea if one can afford it. It doesn't need to be a lawyer (and would therefore be cheaper) - unless you run into some legal issues during the residency process. Mine was a 30-year-old legal issue in the States that wasn't even supposed to be on my FBI report, much less was it supposed to be reviewed by the immigration court here.
For citizenship without any kind of residency first, I'd go the lawyer route, from everything I've heard.