I know a lot of people love GoToWebinar, but I prefer methods where the client doesn't have to download anything to their computer. That makes it feel like a bit of a dog to our people.

Depending on your budget and needs, here are some that we've used and liked:

Instant Teleseminar:
Pros - Low-cost entry, can embed the code on to your own page, public chat room available, very reliable (I've been using it for five years and have never had any failure or technical issue and we've had up to 3,000 participants on this one.)
Cons: Cannot download the replay in video format, but can replay it and embed. Also, this is a powerpoint only type webinar (no screen share or "you on camera")

Meet.fm:
Pros - low-cost entry point, chat, pop-up boxes, can brand with your info, analytics on exactly who watched your replay, versatile - you on camera, powerpoint, play videos, share your screen, do it all. Stable with crowds (we've had up to 3,000 on this one too.)
Cons - no embedding, a little buggy on the audio (guests sometimes have to use the phone in option.)

WebinarJam:
Pros - One-time investment instead of monthly, nice "wrapper" for Google Hangouts, dynamic - lots of functions and lots of ways to share info.
Cons - Higher learning curve, higher one-time investment

22Social:
Pros - Easy to use (registration page, view page are one), Nice templates to choose from, reliable and sound (no tech issues ever), dynamic (too many options to list including a built in affiliate program.)
Cons - Facebook only (but if this is where you are meeting with your audience or if you are selling a social media product, then this is THE tool.)

There are so many more out there, but I just wanted to share those I have personally used often.

Best of luck with your research and your project!

You're getting great advice here already. One caveat I would add with regards to the number of affiliates is this . . . it depends what your time is worth and who is doing the actual "writing of checks."

If you are using a service like Clickbank where they issue the checks or if you have a bookkeeper who does this for you, no biggie. On the other hand, if you're doing it yourself, you might want to give some thought as to how wide you go. It always sounds great to have 1,000 affiliates, unless you're writing out 977 checks for $7. It's been been addressed in this thread already . . . do what you can to get quality over quantity. As Ali mentioned, there is no negative to having EFFECTIVE affiliates.

It sounds like you're good at relationship building and that will serve you really well in a product launch.

Inspire your affiliates to send their first email on "launch" day, which makes it look like "everyone" is talking about it. Keep them motivated with contests and leader boards. (Never underestimate the power of the iPad. Lol.)

If you know the personalities involved and the rivalries, reach out in personal email and egg them on . . . "Man, you're only 2 sales behind so-and-so! I thought you'd like to know how close you are!"

And as it's been mentioned here . . . make sure you've got an offer, upsells, etc. that deliver. Nothing motivates affiliates more than when you can show them the money!

Have fun with it and good luck to you! :) Dana