The golden rule of HTML/CSS coding - your code must be valid. If it already is then there should be no (or very minor) differences between what your site looks at most recent versions of Firefox/Chrome/Safari/Opera/IE9.
If you are sure that you have done everything correctly but still have any problems in other browsers other than IE then you can use Javascript Navigator object or some functionality of Javascript jQuery lib to detect specific browsers. Note that for this to work Javascript must be enabled in client`s browser (imho not a problem since 9x % of users have it enabled).
On the other hand, the best way to solve IE6/7/8 problems is to use conditional tags as you have already done.