Eamon is neither easy to spell nor common.
If i heard it and had to spell it I would try it numerous ways:
Emon, Emonn, Eeman, etc.
I have never heard of it. It sounds cool, but I wouldnt call it common (at all).
I really dont care for the numerous incarnations of Quinniillliinnn, et al. Has fartknocker written all over it. If you're FOB and half your living relatives are in the 'old country' then you could get away with it. Stiller is of Irish ethnicity, but I dont know how far back that was. Were all from somewhere at somepoint. If you arent tight with the culture but get all tight with it in name only, you are just trying too hard and again, its fartknockerish.
Joel works tho.