There are lots of places to advertise but it depends on what market you are going after.
If you want to have a market of gaming sites you will be advertising in a different way than you would for a business site.
Forums are a good way to advertise, join up on some forums which are for your target market and start posting there and you can link to your site in your sig.
You can also submit your company to free and premium hosting directories which is obviously going to be very targeted.
Google adwords works for some sites but not others, think it may depend on your advertising campaign.
You could offer free hosting for sites and put your banner on their websites (I wouldnt recommend this...it hasnt worked well at all for me but I was aiming more just to offer a good free service rather than as an advertising method.)
You could advertise in your local area, ring up local businesses, post flyers etc. This can work quite well and you can normally charge more in a local area than if you were going to compete on the net with a load of other companies in the same area as yourself.
Hope this helps