I promote a lot of websites. Quite a few of which seem like great ideas at first but end up never taking off. This is true for most site owners. You at least have a couple dead sites sitting there. If you’re not at this point yet, remember this one piece of advice. Keep the deadbeats. They will someday become useful to you. Even if they aren’t going to make you any money you can at least get more use out of them than if you let the domain go to a domain sponsor.
I developed a technique for turning these deadbeat sites into great rankings for my newer more promising projects. Chances are these sites have a page rank. Use them. Even if they are small and on the same Class-C IP as your newer sites you may still use them to boost your rankings for your newer projects.

You have several options rating from good, better, best.

Good

Link to your new site on every page of your old site. This will help boost your Page Rank, but probably will do very little for your rank in the SERPS because search engines tend to discredit the same outbound link on every page of a site. Especially if it’s to a site on the same server. This however does tend to work very well for MSN.

Better

Use the deadbeat sites for incentive in link exchanges. Ever try going to a major PR7 site and asking them to exchange links with a PR4? Doesn’t usually work does it? Instead offer them a link from a PR5, PR4, and six PR3’s for example. Give them the addresses and let them know that these extra links will definitely be worth their while. I personally have managed to get many very high ranking, high PR sites to link to me this way. Trust me this actually works very well. What’s the worse that can happen? Your dead site gets cluttered with a few links? Big deal. This way you both win.

Best

Repromote these sites so they pull a good page rank. Then signup with a company that offers their advertisers text link directories on other sites. I’m not going name any particular companies because I don’t want them to get flooded with requests, but there are quite a few out there. Once you have their directories uploaded onto your site and the next Google update gives the directory a decent page rank, come to them with an offer they can’t refuse. I will give you UNLIMITED links on the directory as often as you’d like in exchange for you sponsoring me a PR8 link(or whatever you think your directory is worth) on a site that’s on topic with my newest project. If your directory pulled a decent page rank they will literally jump out of their chairs at this opportunity. They normally have to pay you around 5 bucks for every link they place on your directory. They also almost always have an excess of links they need to place and are looking for a cheap way to put them up. If they can dump all their excess links in your directory for free, they can make WAY more money then they will spend paying a high page rank site to put your link up permanently. Remember, they do get them for half price after all.