A pair of zebra dart fish is always fun to watch.
If you have enough space a few yellow headed jawfish in a tank is well fun to see, must be yellows as blues will not live together, but once settled they will all bob in and out if the sand bed together.
I agree with Ben, buy a small pair of juvies - and watch them choose who is going to be the boss
However there is a caveat, on occassion you get real mean orchids who will not accept another in the tank, even if they go into together as juvies so as long as you are prepared and equiped to whip out one to a qt tank or box etc then go for it
That's good to know there not overpriced on these but still £60 for two fish I think after my R.E exam tomorrow I will go and ask them to get me a pair of clowns maybe the black and white ones with the orange noses there pretty cool