Hello Marjon & Welcome to the SSWT Forum!
I recommend for domain name registrations - $8.95/year and great service.
Personally, I prefer the .com extensions, with .net running a close second (if you have a need to develop both - but I wouldnt recommend registering the .net if the .com is already taken by another company).
While I agree that researching keywords and using hyphenated domain names is a good option - you might also consider branding. Think GoDaddy, Google, Yahoo, eBay - short domain names that dont necessarily relate to the content on their sites.
Keep us posted!