You might probably have several topics you like to blog.

Instead of having more domain names for several topics that you like, it’s cheaper as well as more beneficiary to make sub-domains from one main domain name. you can have as many new domain names you want from that one domain name.
Pick several of blogging topics you like and find the correct and shortest keyword for that typical topic and start a sub-domain using that keyword, the shortest the better.

Example :
main domain : http://www.intinfos.com
Topic : Make Money from Your Blog
Sub-domain : http://wisdom.intinfos.com
Sub-domain : http://ebooks.intinfos.com

Why sub-domain?
Sub domain is one of the many ways you can improve your site’s popularity and links.

SEO companies are also on this sub-domain sites, and GOOGLE loves this. Have you ever noticed how many sub-domain name GOOGLE has?

tools.google.com
search.google.com
blogsearch.google.com
pack.google.com
images.google.com
and many more …

Now, start making sub-domains instead of buying more domain names you can’t even find it easy to manage.