One of my favourite apps is
AppsGoneFree. It highlights 5 or 6 short term free apps every day, and although theres a LOT of cruft and you might not spot something you want for ages, eventually something will turn up. I have acquired PDF Expert, Notability, and quite a few other productivity apps in this way. I also have a bit of a thing for hidden object games, and those turn up very regularly, happily. Weekends are usually reserved for kidstuff. anyway, Apps Gone Free is a really excellent resource. Its universal, for iPad and iPhone.