*edit* In view of the streaks posters have posted before, this has sort of become rank the top 10 player win streaks.
10th Best: Svetlana kuznetsova
wins: Fed cup (2 matches), Tokyo Final (If not for Fed cup which is technically ITF I think, Kuzzy's longest and most recent win streak is her French Open Semi = 5
9th Best: Vera Zvonareva
wins: Fed cup (I match), Guangzhou, Beijing Semi.
8th Best: Agnieska Radwanska
wins: Pattaya, Doha Semi.
7th Best: Ana Ivanovic
wins: French Open – Wimbledon 3rd round
6th Best: Venus Williams
wins: Wimbledon – Olympic quarter
5th Best: Elena Dementieva
wins: Olympic Gold and US open Semi
4th Best: Jelena Jankovic
wins: Beijing – Stuttgart – Moscow
3rd Best: Dinara Safina
wins: LA – Montreal - Olympic final
2nd Best: Serena Williams 17
wins: Bangalore – Miami – Charletson - Berlin quarter final
1st Best: Maria Sharapova 18
wins: Australian Open – Doha – Fed cup (2 matches) – Indian wells semi-final.
Maria's streak was most impressive (BUT If not for Fed cup though, Serena has the longest streak
). Bar the loss to Kuzzy, she went on to win Amelia Island too. Surprised Jelena's isn't longer, I thought winning 3 titles in a row would put her on top, but guess it's down to the events she won needing only 4 wins at a time.
Honourable mentions to Errani and Dokic amongst others for their impressive runs, though sadly they do NOT meet the criteria for a ranking in this list. But a round of applause to them please