I thought Chmoogle was nice when I blogged about it a few weeks ago.
But QueryChem takes open content chemical searching to the next level and here is why:
1) Just like Chmoogle, you can use an editor to draw the a molecule or type the SMILES code as input. But you can also add text queries to fine tune the results. For example, typing "CAS" in the text box pulls up only those hits where the CAS number is likely to be listed.
2) This is the big one: the results in QueryChem take you directly to the pages of the commercial suppliers. In a Chmoogle search, the results only take you to the general company URL, where you have to do the search over again.
3) A QueryChem search does a lot of work for you. It figures out the possible names for a compound then throws that back into Google or Google Scholar and then shows where those names appear in the results. That saves a lot of manual labor.
4) Compound analogs also show up and the threshold of similarity can be set in the search.
With all of these advantages, QueryChem is now my first choice for single search open content chemical information. For ongoing monitoring of our UsefulChem project I am still going to use CAS number searches in MSN (exportable via OPML) because QueryChem does not yet provide RSS feeds for searches.
Another feature that I would love to see in QueryChem is the ability to form a URL of a given search.
Update: Justin Dale Klekota from QueryChem has just enabled forming a URL for a search. For example the search below formed by searching the SMILES code for glycoaldehyde and "CAS" can be called up by clicking on this link. He also informs me that they are working on RSS feeds for searches. How is that for responsive!