The font size in the sidebar shouldn't be larger than the font size of the main text in the centre column, and the main text in the centre column should *definitely* be larger than the ad text. The centre column should be visually more 'present'. Perhaps a variable width rather than the current fixed width, and a centered wrapper rather than the left-aligned one.
The three-column layout is hard on the eye on a fixed-width.
Also, there doesn't need to be a double border between columns if the sidebar boxes already have a border of their own. The mess of vertical and horizontal lines detract from the already busy page.
If the sidebar boxheadings have rounded corners, then there shouldn't also be a styled border around them to take away from the rounded corners.
Have a button on the page that allows people to increase/decrease font size.
Have a button on the page that allows for a printer-friendly version so that people don't have all the images and ads on a print of what they want.
Ditch today's date. Add a 'page last updated on' script instead if you must put some date on it.
Less text on the home page. The current article on the front page is irrelevant to the index page. Make links to 'featured articles' or something like that instead, so that there are less words on the main page, but more options for navigation instead.
If people don't find what they're looking for on the main page within a few seconds of their arrival, they're gone again. Make the main page uber clear for navigational purposes.
Categorize the various animals (dogs/cats/birds/fish/etc). People who are looking for dog info might navigate away when the first words they see are about domesticating feral cats.
Have a 'site index' link on every page.
See if there are more integral alternatives to the Google search box, something that continues the site's layout even on search pages.
See if the forums can be more integrated to the main layout of the 'regular' pages. As in, more cohesion, and more access to the main pages from the front of the forum pages. Scrolling down to the bottom isn't an optimal way to get people who land on the forum to see/access the main/regular pages. Perhaps a nav bar at the top or a similar 'site index' link.