Personally, we have thought a lot about marketing in terms of social media, viral campaigns and even targeted localised door drops and those are being actioned as necessary.
social media - use twitter as a customer care and advice and promotion tool - special offers, allow customers to ask questions about their orders or products. use facebook to gather fans, implement sharethis on product pages and on the thank you after checkout page (I just bought this Washing Machine from YourShop.com)
viral - not really feasible for ecommerce. viral stuff is more for brands.
door drops - waste of money for anything on the internet.
are customers coming onto your site to research, or to buy? where are they coming from? check out your analytics, because they'll show some unusual entry search terms normally.
optimise your site for conversions. how high is your bounce rate? start with the page with the highest bounce rate (excluding homepage) and start optimising it for conversions.
implement behavioural merchandising, whether in the form of a simple magento plugins or a more advanced service if you have a lot of traffic (like PredictiveIntent)
PR - think about where you want to position your self - niche, not the cheapest, or cheap and cheerful? if niche, target bloggers in the field, offer them samples in exchange for reviews, if cheap and cheerful, do something really wacky that could get in the Sun or something).
are there any events you could sponsor or appear at, like trade shows etc.
optimise your email marketing - segment, make it really relevant, push visitors into signing up for your newsletter for a discount code or something.
make sure your site can be accessed properly and that orders can go through on iphones, android phones and blackberrys. people with those phones expect to be able to access any website without trouble, people who don't have those phones aren't in the same mindset to buy online so you don't need to worry about symbian etc phones.
make sure you've done everything else, like one page checkouts, "free" delivery (include it in the prices)
make sure your datafeed is on google shopping. just list your site on as many shopping directories as you can find on the net - both for SEO and because they can give a trickle of traffic.
PPC - try microsoft advertising because they do yahoo too and are cheaper than google - and since msn is the default homepage for most computers, people might just search straight away from there.
make sure you've got fuzzy searching, either done manually/basically or done through a proper service like FACTFinder.
optimise your transactional emails - upsells, cross-sells, forward to a friend discounts.
make sure you're writing on your blog about the products you sell - these should help you for general SEO and for catching some general longtail keywords.
ummmmmm.........
i think i'm going to write blog posts soon about every method which could help optimise conversions and every way i can think of to get traffic...
