If we're talking longest odds, i remember taking glen johnson rounds 7,8,9 and 10 vs Roy Jones at 100/1 for each round.
Also Prescott 80/1 rd 1 and covered the first four I think, but someone else got 125/1 I seem to remember. Oddschecker wasn't in my life back then
In terms of most satisfying, enzo KO1 Bobby Gunn was good because I accidentally refreshed the page or something and somehow put on £200 instead of £100 :)
Calzaghe PTS Salem at 5/1 was a good one too, it was my biggest ever bet at the time and I was still at uni. I persuaded my mate and a few folks on boxrec to get on it too.
Fond memories :)