The .ie domain signifies to people that your site is Irish. This is especially important if your domain name is somewhat generic e.g. Doubleglazing.ie versus doubleglazing .com. However if your business/domain name is DublinDoubleglazing for instance it's far less important to have the .ie domain.
Also if your audience/customer base is international the .com domain may be better for you anayway.
Don't worry about Google results with .com domains if you're hosting your site with a hosting company whose servers are based here. Google can tell where your site is hosted and that will affect your rankings on the country specific google domain (e.g. .com sites hosted in Ireland will typically rank better all things being equal that .com sites hosted in the USA or UK ).
Not to get too techincal here but if you do buy both domains - .ie and .com make sure that one of them is redirected to the other by means of what's called a 301 redirect (your webmaster should know what this means if it's double dutch to you). Otherwise the search engines (google really) will see your site as two different websites and they don't like that too much.
For your type of business, which I assume doesn't have an international dimension, I'd say .ie is best, partially for reasons already mentioned, but mainly for the marketing aspect of it identifying you as a local company.