How do I get WordPress to not insert tags in PHP output?

I’m inserting some PHP code in a page and I can’t get WordPress to stop putting <br /> and <p> tags in the output. I tried three different PHP plugins –
Exec-php isn’t good because it requires turning off the visual editor.
Inline-php works well, but WordPress was inserting p tags all over the place
PHP-execute was what I ended up using, but there’s still tags being inserted. I ended up just playing with formatting to make it work ok for now.

I need a way to be able to insert PHP into WordPress without having to change settings that will affect the rest of the site. Does anyone have a good technique? Perhaps a Server Side Include?

Thanks