New answers tagged user-interface
A simple mock credit card is an alternative to the standard paper/coin icons. Even something as simple as a rounded rectangle, with an offset black stripe could be enough to express what you are trying to convey.
What about a hand holding a bill? A bit of a complex icon, but I think it can be an option. Anyway, in this context I would choose coins too.
I would go with coins, hands down. You do not have to make it a "pile" - a few shiny circles should do. Consider, coins as a term is not going to get out of "fashion", as exemplified by bitCoin.
I think it depends on who your target audience is, beyond geography. If they're moderately tech-savvy, I think either of the three would work. I'd lean towards the shopping, as it is the most used for online purchases, and has the most positive connotation (take this with you in your cart, as opposed to part with your money).
In the specific case of MailChimp they have made their framework available for public use here- http://ux.mailchimp.com/patterns/ You will also find nuggets of their design process in their blog articles and if you subscribe to their newsletter. They also warn that it isn't like Twitter Bootstrap and a lot of it has been tailored to have suited their needs. ...
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