So at present we have the following used in the puzzles (at least, those I have seen)
+add -subtract x-multiply /-divide(the proper symbol isn't on my keyboard)
^-exponent
mod-modulo
|-bitwise-or

I would like to see some more operators in the puzzles, and suggest the following:
& bitwise-and
bitwise-exclusive-or; not sure what symbol(s) to use - perhaps &|
< less-than: seems best to make it work on two cells only, and the LHS must be less than the RHS cell; Two cells above and below could use the V where the upper is more than the lower
> more-than; like less-than but the other way round

Another thing to make different puzzles would be to have one number from the series missing. For an example, a six-by-six puzzle could be made using not 123456, but instead 123567. Two approaches come to mind here
(1) state with the puzzle which set of digits are used (in my example it might say "1 to 7 but missing out 4", or
(2) just provide sufficient info in the puzzle to solve it by analysis (in my example, one row that multiplies all the digits together would have the clue "1260x")

But, I'll still keep coming back for more puzzles each day, even if none of these are liked or practical. Great site, thanks for keeping it going.

Good suggestion, randomfruit, see this link, for instance.

viewtopic.php?f=16&t=124

Thanks for the suggestions. I thought that bitwise AND (& in C) and XOR (^ in C, so easily confused with exponentiation) were too similar to OR (?)

The less than/more than conditions are possible (a Calcudoku - Futoshiki combo then really),
but quite involved to add that to the software.

And yes, I would like to see an arbitrary set of numbers, so even {2, 3, 5, 8, 10, 25} for example (instead of {1, 2, 3, 4, 5, 6}).
I did start testing software for this a while ago, but again, it's quite a big programming job,
so I'd have to find the time for it...