I imagine you hand registered those domains, and that's fine, but look at it this way. When you hand register a domain, it's just a name, you could hand register hibbertybobbertyflump dot com which means nothing to nobody, unless you build on it. Basically any domain can potentially be worth anything, most domain buyers don't just look at the name, they look at the alexa page rank, back links, the age of the domain etc.
For example, before instagram and facebook, consider how many people would type those names into a google search or their address bar? now look at where they are in the consciousness of people and consider the fact these names are only popular because of the content behind the name, these are 'brandable' domains.
To sell a domain based ONLY on the name, it must be very targeted and also targeted towards a popular and fluid market, these tend to be one word dot coms for the most successful sales, but to invest in that part of domaining you need thousands of pounds, say 10-30k to get started.
The other kind of domains that are targeted are clever keyword rich two word dot coms (easier to hand register) or geo domains as mentioned previously, city or country name + profession can yield good results for people (so i've heard) the hard part is convincing the end user to part with their cash and for that you must be a salesman making phone calls, sending e-mails and networking.
Another method is domain parking or building a blog or mini site relevant to the subject of your domain title, the aim here is to build traffic to the site, generate revenue from PPC advertising, so even if after a year it doesn't sell, you may have just about made back the initial investment you made in hand registering the domain. This also helps to give other domainers a good idea for the potential of the web site, you are essentially 'proving' the concept.
Everyone thinks they have chosen the best domain names, but the ones who sell them and make a living make efforts to prove their concepts.
I haven't mentioned the LL, LLL, LLLL, domains because these tend to be for those who have deeper pockets, and with that carries a greater risk. You could buy a LLL for £5k and never sell it again for more than £5k, you may end up selling it for £4k.