Yelp is a good one for general businesses. Ultimately is there any reason not to be on Yelp and the answer is no. It takes a few minutes to submit your businesses details and it maybe, might, just help to create some business for you.
Yelp frown on you asking people for reviews and want it to just happen organically. Don't really know how feasible that is in Ireland though, unless you're maybe in the hospitality/tourism sector.
On that note, sector specific sites can be huge - Trip Advisor would be huge again for those in hospitality and tourism sector. There are a host of Tradesmen sites, most of which are subscription based, but they can have a good number of reviews on them too.
Leaving aside the niche sites like Trip Advisor, here's my rankings for the most important review sites -
Google My Business
Facebook Business Pages
Golden Pages (very unlikely to get a review organically, but if you do it can help a little)
and then the rest
Realistically you are not going to get too many reviews on all of the plethora of other directory sites, but its still worth submitting yourself to them - they provide your business with citations and backlinks, which will provide your website and GMB listing with a small rankings boost. Well worth while for a few minutes work.