SR is about choosing what app fits a person's scenario the best (requirements, budget, environment, etc).
So it is easy to come up with the metaphor of shopping. And shopping is the most hated thing on SE. But you have to admit that what we are doing here bears similarities with shopping: someone has a need and a budget, several possible solutions, usually resulting in the choice and adoption of one. I actually designed one of the earliest SR advertisements reading "Shopping? There is a site for that!" and it is my most-downvoted post ever :-)
Another metaphor is consulting. That's actually my day job: helping companies choose the architecture/technology solution that will fit their needs. And before that, help them find out what their actual needs are. Unfortunately, the idea of consulting is difficult express visually without looking boring.
We are all about finding the right tool, so any image of something fitting perfectly could potentially work:
That was actually the idea behind the advertisement that we ended up using:
The wrench idea is convenient but it might feel too industrial/manly. SR is for everyone, not just for programmers. Software is used in all domains of society, so we want to attract software users in all domains: sales experts, finance experts, human resources experts, agriculture experts, etc. A photography expert who has experience with various software suites of the field will be more able to answer photography software questions than a programmer who has only amateur-level knowledge about photography. An ideal logo would suggest this diversity rather than confirm stereotypes. Thinking about it, that's a possible strength of the shopping metaphor.
Similarly, a design showing bits, and 1s and 0s, would probably feel too geeky to attract domain experts. An ideal design would concentrate more on "recommendations" than on "software", because half of the SE sites are about software, but this site is the first one to be about recommendations (as you know, 99% of the SE sites are vehemently against recommendation questions).
A metaphor of tailoring would be misleading: we prefer ready-to-wear.
I am not sure what to think about the metaphor of installation media 
. My new laptop does not have a DVD slot, and I install all of my software via apps stores or PPAs/source. But if the gaming SE is OK with big pixels, some here might be OK with floppies.
Anti-idea:
Rows of software boxes in a shop alley might convey the idea, and it allies the idea of shopping to the idea of software. But it presents software in a way that many of us here despise: reduced to a commercial good. All of us are volunteers, and maybe as a correlation most of us love open source software, which is the anti-thesis of buying a box from a megacorporation.
Recommendation metaphors include thumb up and green check mark 
. Not sure how a design can be made out of that, but a professional might be able to do it without making the site look like an ecommerce scam :-)
Metaphors for consulting could be the best source of inspiration:
Here a consultant found a puzzle piece that fits perfectly to the asker's scenario. The puzzle idea might actually be my favorite so far.
Here a single light bulb works correctly. More nuance would be welcome, for instance with various brightnesses/shapes.
Here a single path leads to the exit. It is more about strategy, but sometimes that is what we are doing here, for instance migration route recommendations.
Here a bunch of smart-looking people are talking with passion. The most typical representation of consulting.
