Here are some useful tools that i recommend:
I've been seeing a lot of multimedia stuff in the recent past, so I thought this may be a good resource for people to use. This is a free online service that lets you rip multimedia from a variety of sites. It will also convert the multimedia file(s) to a variety of different formats. All you need to do is fill out the fields and it will email you the link to grab the file you wanted (in the format you want it in). It's a pretty nice time-saver.
One of the best free Internet Marketing research sites I have seen. Provides a variety of features that can give a competitive edge to anyone in any niche. The only drawback is you sometimes need patience. Depending on the service you use, the queries can take a long time to complete.
Oldie, but a goodie. Marketleap allows you to freely research sites by seeing where all
of their inbound links are coming from in AOL, Google, Yahoo and MSN. Find out who's linking to your competition, perform link trades with them, and gain the competitive
Pretty much figure out anything you want about a domain name. Ever wanted to figure out what sites the guru's own? Well, if you're willing to pay some money, you may be able to figure this out as well. Providing the guru's run their sites on dedicated servers, you can buy a Domain Tools membership, perform a WHOIS lookup on one of their sites (i.e. a product sales page), and then discover all of the other sites running on that server through Reverse IP. With a little digging and creativity, you can also figure out a lot more about your competition through this one site!
Hopefully people will get some use out of these. I know they help me out!