Eley Trap 14gm 2.5" but really you should be using Fiocchi 19gm 3" if your gun has the chamber, easily the best. Beware traditional English 2.5" - not up to the job.
Hamish - if your planning on shooting some skeet with .410 then i would recommend the Gamebore target load in .410 - they are easily available from Just Cartridges / your gamebore stockist and perfectly adequate and in fact many of the NSSA skeet shooters here in the UK use them in competition (Myself Included).
They are a 14gram 2.5" shell but only come in 9 shot i am afraid - price is about £7.35 a box of 25.
As for non skeet .410 loads then i hear good things about Eley but no experience with them so cannot pass personal judgement.
The out and out winner in 2.5" .410 cartridges is the Remington but seriously expensive for what you are hoping to achieve i suspect.
Eley, game bore or saga, I've found nothing else that is worth a light on this side of the Atlantic. Would happily compete with any of these three and you shouldn't have a problem locating at least one of these. Don't waste your money on anything else.