I haven't read any of them yet, but I do own books 3-7 of The Hollows. Right now I'm around 250 pages into The Mortal Instruments: City of Bones, so far I've really enjoyed it. I also picked up the first Iron Druid Chronicles book, Hounded. Hounded and Every Which Way But Dead are going to be two of the next things I read. The second Kate Daniels book, and the 7th Dresden Files book are my next planned purchases.
EDIT: I decided to splurge and I picked up Dead Beat (Dresden Files #7) and Magic Burns (Kate Daniels #2), which are immediately jumping towards the top of my to read list.
In the next few months I definitely plan on reading:
Hounded (Iron Druid Chronicles #1)
The Hollows 3-7
Bitten (Women of the Other World #1)
Dead as a Doornail (Southern Vampires #5)
Moon Called (Mercy Thompson #1)
Kitty & the Midnight Hour (Kitty Norville #1)
Rosemary & Rue (October Daye #1)
Midnight Riot (Rivers of London #1)
City of Ashes (The Mortal Instruments #2)
Artemis Fowl (Artemis Fowl #1)
Percy Jackson & The Lightening Theif (Percy Jackson #1)
I might also check out:
Magic to The Bone (Allie Beckstrom #1)
Ill Wind (Weather Wardens #1)
Night Shift (Jill Kismet #1)
Obviously this might change if I burn out on UF or find other stuff that interests me more.