It depends of course to whom you are writing. When I write to the family I grew up in (parents, cousins, sisters, brothers), I sign off "Love, Charles". For my wife or children, "Much love" or "Hugs and kisses" and "XOXOXO" as Shawn suggested would be fine. These would work for boyfriends/girlfriends and probably between two female friends as well but my male friends would be taken aback by such open expressions of intimacy. Between male friends, "Warmest regards", "Yours", "Later", "See ya'", etc would work better.