Incubator Y Combinator just wrapped the first of its two West Coast demo days for its latest batch of startups. As usual, their concepts were all over the place, from ticket sales to retail polls to job listings.

The startups gave demos on the East Coast last week (Y Combinator’s summer session is held in Boston), and there has already been some debate about whether there were any “winners.” One grumpy attendee reportedly told Silicon Alley Insider he was unimpressed by the entire lineup, although other commenters (including Y Combinator founder Paul Graham) begged to differ.

As for me, well, I have to admit I found the lineup less exciting than the companies that demoed in March. Most of the products seemed solid, but from a conceptual perspective, I just wasn’t as jazzed about them. A lot of the startups seemed to be “like FILL-IN-THE-BLANK-COMPANY, but easier,” which may make sense as a business model, but makes it harder to pick winners without actually trying the service.

Still, there were a handful that jumped out at me as particularly promising, or at least fun and interesting. Here are the five that made the best first impression, in order of preference:

1. CO2Stats — Dubbing itself as “the VeriSign of sustainability,” the company offers a way for websites to certify that they are environmentally friendly for a monthly fee. CO2Stats analyzes the energy footprint of your website (which is a really cool tool in and of itself), then purchases an equivalent amount of renewable energy to offset your usage. You can then place a button your page attesting to your site’s environmental friendliness. The company says it already serves 2,700 customers (including IBM) in 25 countries.

2. Posterous — A service that makes it easy to blog by email or text message. Users just send the text, photos, audio, video or other attachments to post@posterous.com, and Posterous publishes a blog for you. You don’t even have to create an account. Posterous integrates with blogging services like WordPress and Movable Type, and also with social sites like micro-messaging service Twitter and photo-sharing site Flickr.

3. Slinkset — A service that lets you create a branded, customizable site where users can vote content “up” or “down”. One of the obvious applications is the creation of social news sites (”Reddits for the masses”) but Slinkset can be used for any content you want. Similar services include IdeaScale and UserVoice. What I like about Slinkset is how fast and easy it looks to use — the founders threw up a branded polling site in two minutes during their onstage demo.

4. Job Alchemist — A job listing startup that combines two different services — niche listing sites and an ad network for job listings. Neither idea is all that novel, but Job Alchemist seems to be have a solid offering on both sides. Startuply, the first of its niche sites (it focuses on startup jobs, of course) has already launched. The listings network — which will be called JobSyndicate, will pay a healthy reward