Any domain name registrars out there that support domain name registration using a web service or a similar functionality without them telling you to become a reseller?
I don't register that many domain names and I am not interested in paying reseller fees.
If I can become a reseller without paying upfront fees, that would be fine.
www.opensrs.com charge a one-off $95 setup fee. That's not quite what you asked for, but it is pretty low. You get access to a well documented, functional API. However you need to pay for domains by making a credit to your account, then buying the domain from there. I don't think there are any limits on how small this initial deposit can be.
Despite the unfortunate name, NameCheap.com have been really good. I've moved all my domains to them and I've found them to be the best registrar I've come used.
They also have an API (developer.namecheap.com), which is free to use - although you have to either have $200 or greater in your account, have spent $200 in the last two years, or have 20 domains in your account.
I've only just started with the API, but it seems pretty good so far.
I looked at the APIs for several registrars when I was working on programatically registering domains. My needs were basic - I just wanted to register a domain name... not change ownerships, forward URLS, check the weather, or all the other bells and whistles.
I ended up using Moniker.com and found their API to be simple and straight forward. I read their docs and was up and going within an hour.