what are the best methods to promote online products?

You could always follow your own advice in your other posts about SEO

So many good ways, from social media to making videos to even using traditional marketing efforts (postcard mailouts, billboards, pub crawls, etc.) to promote your website online.

I agree with what's been said above, social media is a very effective way to advertising your business. Also social media, I'd try advertising your business in many way as possible.

I think a lot of people don't realise how hard it actually is to maintain an online business. Granted, it's probably easier than a physical one, but still difficult.

Although it might be more cost effective to promote online, I wouldn't scrimp.Your products or services have to be of the best quality. If it means spending more on Marketing or your website - then so be it.

I recently downloaded James Caan's Business app and there was some really useful information on there about online businesses (Here if you're interested)

He said something about treating your website like a grocer's shop window - make sure your best apples are at the front. Makes sense when you think about it!

I`d go for all possible options - both online and off line, as as discussed in another thread both forms of marketing are important for each kind of business.

Promote online product,
Direct mail: you can send direct mail to the your targeted customer for providing information about your product.
use Social media: Create create profile pages with the name of company for products promotion.
create your business blogs
Social bookmarking for your website.
Create 'Groupon'
Use Google 'adwords', Microsoft 'adCenter'
Conduct online survey regarding your products and suggest your product to the people.
use proper Email Signature.
Make classified adds along with discounts relate to the occasion
Provide online coupons through the various contest.

If you need some free traffic to begin with then use sites like YouTube, Quora and Yahoo answers to drive traffic. There is plenty of traffic to be lured from those sites and it won't cost you a penny to get started.

People seem fixated on generating traffic to their website ....you hardly ever hear anyone mentioning generating orders and enquiries from their website. They just shout about how many "hits" they get, and some use the proper word and tell us how many visitors they get, but you rarely hear anyone confirming what orders they got from their site this week, or how many contact form enquiries or calls and emails generated from the website, this month, etc.

does anyone have any success with their own online shops or do most people use marketplaces like Amazon and eBay these days?

I was talking to a guy who sells clothes and he reckons that he gets very little business through his own site now, most of it comes from his online shop on Amazon.

Downside is there is no customer loyality, most are just interested in cheapest prices and if you're a seller with a good rating or if you have an exclusive deal as a distributor from a manufacturer.