Hopefully if enough of us answer, this could be a decent point of research.

Current Registrars:
eNom.com [ETP] @ $9.95
Moniker.com @ $6.85

Registrars Used:
NameCheap.com [eNom reseller [though may become ICANN-accredited]]
RegisterFly.com
Nomanix.com [eNom Reseller]
ev1servers.com

Ratings:
eNom.com: 4.5/5, the other .5 is because you need a thousand or so domains to get the same pricing as Moniker. Great interface & reliability. Support is professional albiet slow (something around 9-5 on weekdays), but not an issue if you only need to contact support twice a year.
Moniker.com: 4/5, great pricing, Monte (the owner) is friendly & a member at WHT and dnForum, though the interface isn't as aesthetic as eNom. Works well for small or large domainers, and has many unnamed security features.
NameCheap.com: 3/5, was not too impressed with their support, though the interface is nice & works well enough.
RegisterFly.com: 2/5, nice interface but slow as can be. They would be a 3/5 if each page didn't take forever to load.
Nomanix.com: 3/5, standard eNom interface for a reseller, never had any problems with them.
ev1servers.com: 2/5, cheap pricing, but their interface was terrible.

Total Domains:
Under 50 [I develop names, I don't resell or buy in bulk.]

Keep all of my 10 domains at NameCheap. I like their easy to use interface unlike godaddy.

Welcome to WHT, HrvDin. NameCheap's interface is nice.

Moniker.com @ $6.85
How do you get $6.85 pricing from Moniker? The cheapest I see on their site is $8.95 if you prepay $1,000.

You have to create an account and email them asking for forum pricing.

Enom, their interface is slick, easy, stable and top notch.

all enom. A couple in my enom reseller account, most in namecheap.

RegisterFly.com (6.85 /ea) - I like the security tools
enom.com (6.95 /ea)

Between the both of them I have about 7900 names (give or take a few)

I really like Enom's interface, but sheesh, $$99 a year to use their API? What is this, 1995?

Directi lets you use the API for free, but their site is sluggish (glacial?) and their way of doing things makes no sense to me yet.

Godaddy has the pricing right, but their cluttered, constantly up-selling interface has turned me off. I think their policy of deleting domains upon any sort of complaint could be harmful at some point too. Their reseller API is even more expensive and restrictive than Enom.

Are there any decent registrars for resellers, with good pricing and a standard API?

eNom has a free program (RegistryRocket) and anyone can use their API.. PDQ is $99 and looks nicer + lets users manage web hosting and some other stuff.

eNom has a free program (RegistryRocket) and anyone can use their API

I don't believe registryrocket is an API. It doesn't work with hosting carts and billing systems. It seems to be just a web page if I want to let Enom sell sites to my customers and keep all the money.

Sorry, I mis-worded the post.

eNom has an open API. The documentation is available to all resellers. It works with PHP, Perl, and a few other languages.

RegistryRocket is software built on the API that you can install on your site--mainly for people who don't need/can't afford PDQ, and don't want to code their own system.

PDQ is also built on the API I believe, but allows users to manage websites and other features which the API does not allow for (or RegistryRocket doesn't include--not sure which).

I keep mine at Godaddy.

my .com`s are on GoDaddy and .info`s on registerfly.

I have quite a few at GoDaddy, and quite a few at DirectI ;)

My company is an eNom ETP and we keep most of our domain names there. The rest are at GoDaddy which we are slowly moving to eNom.

Dan: the 6.85@moniker without prepay?

Yep. You have to email them for that price.

All my .uk's and most other TLDs at 123-reg.co.uk and a few domains at ev1servers.net and 1 or 2 at namecheap.com.

I hate GoDaddy, such a farse editing domains.