I will return to indiegogo when 0.96 comes out. I have trouble thinking up the main text and "awards" for those who will donate 1$, 10$, 100$. Indiegogo can provide some account collecting, so it's possible to use that information to gift a release version of the game (or online account) for generous donators, but I am not familiar with this.
Also, I need a new cool video. I would like to make a tour through SE objects with text describing the technology used for creating these objects.
If you're having trouble thinking of what to write, simply describe what SpaceEngine is, why it's so great compared to what's out there, and why you need the funding. Make sure to stress the fact that you're just one guy - I think that would make a lot more people willing to donate, knowing that it's not a company doing this. Also make people very aware that you already have a working system right now that donators can download and try for themselves. This makes people know that you will actually be able to offer what you promise.
As for perks, that is a hard one. I had the same issue with a friend when we started an IndieGoGo for a website. It was a .org, we didn't make any money off of the website and we didn't sell any products, so what could we have used as a perk? Well, in retrospect I don't think we did that good of a job choosing perks, so I won't use that as an example. So some ideas for SpaceEngine are: For lower donators, they will get their name on the credits list. Maybe slightly higher, they will of course also get their name in the list, and also maybe a personal thank you note from yourself. For higher donators, they could get early access to features you're in the process of adding. For the highest donators, maybe you could add a personalized planet just for that person in the game. I think that'd be awesome.
Anyway, those were just some ideas so hopefully you might be able to start funding on IndieGoGo soon. Hope that helped.