This SPOJ Problems Classification 1 tool provides information about SPOJ problems and associate them with a set of tags.
Also check Facebook note.

This SPOJ Problems Classification 2 tool provides information about SPOJ problems and associate them with a set of tags.
Also check Facebook note.

SPOJ Backup Tool allows to download your submissions to local disk.
Also check github repo, this thread and Facebook note.

SPOJ User Statistics 1 tool shows interesting users stats.
Also check Facebook note.

SPOJ User Statistics 2 shows users stats and allows you to compare two users.

SPOJ User Statistics 3 shows users stats. It works with English, Portuguese (BR), Vietnamese and Polish versions of SPOJ.

SPOJ Utilities provides users stats and more.
Also check Facebook note.

SPOJ Rank Tracker - Firefox add-on that tracks your position in the main SPOJ Ranking.
Also check Facebook note.

bbone - phpBB add-on that allows to execute submissions directly from posts - installed on SPOJ forum.
Also check this thread and Facebook note.