Just dug out my planning notes from several years ago - I think this list may have been supplied by Moth. We didn't visit all of these, but did visit quite a few not on this list. It just shows how much there is in such a small area:

Anglesey Megalithic Sites

This is a circular route you can do. A look at the map around most of these sites will reveal mind blowing amounts of other features to look at.

Over the Menai Bridge, then Westbound

Bryn Celli Ddu; standing stone not far to the N on farmland
http://www.megalithic.co.uk/article.php?sid=24

Bryn Gwyn Standing stones (reputedly tallest in Wales)
http://www.megalithic.co.uk/article.php?sid=716

Barclodiad Y Gawres (need to pick up the key at tourist info / cafe at Aberffraw)
http://www.megalithic.co.uk/article.php?sid=1492

Not far N from there Ty Newydd
http://www.megalithic.co.uk/article.php?sid=170

a bit further N Bodfeddan Inscribed Stone
http://www.megalithic.co.uk/article.php?sid=4116

Head W for Holyhead Trefignath Multiple Chambered Tomb
http://www.megalithic.co.uk/article.php?sid=4441

A tiny bit to the N Ty Mawr standing stone
http://www.megalithic.co.uk/article.php?sid=382812546

Then out W towards South Stack - the hut circles; great place
http://www.megalithic.co.uk/article.php?sid=5946

Not far away, the pre-historic goal posts of Penrhos Feilw
http://www.megalithic.co.uk/article.php?sid=1496

You then need to start on the road out of Holyhead, turn left at major crossroads, heading N to begin going around the island. You will pass Fadog Frech standing stone - easily do-able
http://www.megalithic.co.uk/article.php?sid=187825956

A little further on:
Pen Yr Orsedd standing stones, a little distance apart, both on farm land, but tall!
http://www.megalithic.co.uk/article.php?sid=1256679883

Loop around heading east now, you need to go to Llanfechell, which has a lovely trio of stones atop a ridge
http://www.megalithic.co.uk/article.php?sid=2035752060

and a massive slab standing stone near some pylons
http://www.megalithic.co.uk/article.php?sid=4112

head around the coast road to Amlwch, then south towards Moelfre for Lliwgy Burial Chamber
http://www.megalithic.co.uk/article.php?sid=1495

and Din Lligwy Ancient Settlement
http://www.megalithic.co.uk/article.php?sid=1494

I had a great day out on Anglesey (my first visit) with Blossom a couple of weeks ago. We managed to get to quite a lot of sites in a short time, all very easy to access, never more than a couple of fields from the road (the island is quite flat as well so no uphills slogs).