Can only comment on gravitational arcs. The brightest that I am aware of is described in the paper linked here
http://www.iceinspace.com.au/forum/s...d.php?t=161884.
The arcs in Abell 370 and 2667 may also be worth a look, but these things really are are very dim and will be challenging - if they are possible at all at around mag 18+ (integrated). Would have to be a great experience if you could see one though.
Cheers Ray