We have a bingo software page in the bingo section at the above link- this is the parlay bingo site list. Each site listed has a review you can check out, and there are posts in the bingo forum
that may help you decide.
Personally, I've enjoyed playing the parlay slots most at Bingo Vega
and Amigo Bingo/241 Bingo
(bingo affiliate sites). I've made a lot at times off of the Living Large and Bring Home the Bacon (aka Makin Bacon). If you like the 5 or 3 or 1 liners, 3 Times The Riches is usually good, but pretty awful at some other sites. Being able to place higher wagers is key especially when trying to make the higher playthrough.
At the parlay site ( http://www.parlaygroup.com/products/slots/20-line/
) you can try out the slots they make. Now, I've not seen a lot of these in the US but still enjoyed playing them and some have migrated over to a few sites.
Be sure and claim any bonuses offered in the bingo forum here so you can get some free trial or NDB welcome bonuses and always have the support of the staff here when any issues arise.
Now, as for nice slots that aren't Parlay, I really like the slots at the Vista Gaming Network sites (Cyberbingo, Bingo Fest, Bingo Sky, etc...). You can get a free trial bonus from the bingo forum as well and can join up to three of their network sites. I believe that you have to play with real money, not bonus money here and also at some other of the parlay sites as well. But you can play some bingo and win some cash <wink wink nudge nudge>http://www.vistagaming.com/products.html
is where you can go to try out their video slots, arcade and other products. I'll have to say I've made quite a bit playing these slots as well.
Now, these are bingo sites, but they offer much more. I hope you find something you like.