I've been sitting on these for a while and I doubt I'll be working on them anytime soon so I thought I'd share:

1) SMS ordering system for local cafes and restaurants. Give businesses the means to publish a simple menu and let registered customers order by SMS. Delivery and payment details are held on file so only the menu items need to be sent by SMS. Perfect for ordering lunch at work.

2) Live-sourcing. Connect via VoIP (twillio?) to experts who work under your instruction using google docs (or any app if using screen sharing). This is for people who know what they want but not how to create it e.g. business people who need PPT presentations. Could also work for lazy people - dictate that blog post or essay and watch the words appear on screen with near 100% accuracy. More expensive than outsourcing but with virtually none of the problems you'd get on odesk, elance et al

3) group complaints/protests - like kickstarter for complaints. People can create complaints stating:

a) what the problem is b) what they want done to fix it c) the consequences if they don't. e.g. a boycott, twitter/phone/letter campaign, protest outside their HQ etc

Other consumers pledge their support and if the company fails to act, people take action together. Revenue comes from a small membership fee like meetup ($1 per protester ..?) or by allowing competitors of the target company to advertise on the protest page.

4) Volunteer dating - allow charities to host and publicize events where volunteers can help out one evening/afternoon. Singles in the area can register their interest and then go along to meet other singles at the event. No pressure, casual environment and a great way to meet new people.

5) Guess Who on facebook ... this has probably been done ... ?

6) Offline ad-network : match up people with interesting locations to display ads in the physical world with companies looking for unique advertising. You would only accept listings that have something unique/newsworthy about them. As with all marketplaces, the difficulty here would be the chicken/egg problem but maybe you could use listings on the site to advertise the site ...?

7) creative quotes. Simple, web-based editor to let people create quotes like on reddit.com/r/quotesporn. Revenue from partnerships with cafepress or similar.

8) checklist marketplace. Checklists are very useful for reducing human error/capturing best practice. You could create a marketplace where experts in particular fields publish lists of do's and dont's (along with explanatory notes) that can be sold as PDF's for a few dollars. The publishers get revenue, the readers get the benefit of years of experience and expert knowledge.

9) software for credit unions. I haven't investigated this one much but I met someone who ran a credit union that was complaining about how expensive/outdated all the existing software was (in the UK)

10) letsbuyit.com - it failed the first time round, but people are now much more comfortable buying online. Unlike the original, you wouldn't hold any stock/inventory. Simple negotiate and publish the deals, then let the consumers deal directly with the retailer.