reporting software - take database of lots of data, create pretty reports from it. PHBs love pretty graphs.
Shopping cart / catalog - checkout part is important but not a deal breaker. You can use the catalog software you create for your own nefarious purposes as well, so its not a complete waste of time.
Like perk said. A time management type of app. Simplest would be to just track generic work times, of employees, and create reports for that. The most complicated version would be to add in project hour tracking, project management type of tools and then all those supporting reports. Think of a simple version of MS project. example of an online one http://www.basecamphq.com/
unfortunately, when it comes to getting a job, its more a matter of how YOU sell it to them. I walk into many prospective client meetings, not being able to show anything remotely related to what they want done because alot of the work I do is NDA'd to the balls. My portfolio has a literal "trust me" in it. But the thing I have found the most is, you need 2 projects. 1 for the technical guy, which should have some "cool" things that you did, that the tech guy could appreciate. Scraping data from a non-API system (ah BH is worth something but money aint it), 8 way join, 6 remote databases queried via different APIs, whatever else might be Geek Cool. The other type of project you need to show must have lots of graphics and graphs. Corporate looking, use IBM.com as a visual reference. Its really dumb but alot of the time you will be interviewed by really fishing dumb, non-technical, failing upwards, idjuts. They need pretty graphs. Pie charts, bar graphs, line graphs. Throw in some trend analysis and they will love it. If you can accomplish both of those with 1 project, which all the suggestions, you should, then thats perfect.
but really, those "Text spinners, file re-namers, Page generators etc....." would be fine as well, if you explain it COOL enough.