Lough Neagh lake in Northern Ireland is a nice conserved recreational park devoted to sports. Accessing from Lurgan you will find a beach that curves giving several sideshore directions. Flat to choppy water.
There are also other spots around the lough. For example, Cranfield in the north end (towards Antrim) is an option. However, it is exposed and gets big swell during gale force winds, so naturally stay away in strong winds.
Laytown beach is a long sandy tidal beach with flat to choppy and several sandbars. The tide goes far out and can change the shape of the beach and the height of the sand banks. Constant 12 knot NE wind is best. There are areas north and south of Laytown to consider if conditions are not ideal.
Bettystown area towards north has small waves breaking on sandbars but due to tides there are shallow areas with flat to choppy water. Bettystown is crowded during the summer and you should not kite by the carpark (go several hundred meters past it). There is also sewage outfall and wreck to watch out for. Better during the winter, in E winds.
Gormanston beach, where sideshore is NNW or SSE, can be kited all the way to Mosney up north. Towards Mosney you get several sandbars with small waves breaking on them and flat to choppy water in between the sandbars. Winds tend to be constant 12 knot NE.
Skerries has two beaches, one on the north side and one on the south side. The North beach has small waves and chop and is close to the houses, so be careful if the winds are strong. The south side has small to medium waves with shallow access and is good with NE winds.
Rush is located to the north from Dublin and has two beaches, north and south. Both have small to medium waves and are flat in between with shallow access. There are some restricted areas, where you should only launch past the soft sand sign.
A speedstrip for windsurfers at low tide in north to north-easterly winds. Watch the current, especially on ebb tide! At high water, the offshore sandbar produces decent waves. Kiters also appreciate the flat water at low tide, when plenty of teaching goes on too. Despite the strong tidal influence you can always park pretty near the water.