I use Boomerang too and can recommend them too.
Membership Packages here
I'm on the £10.99 Priority 1 package. I usually get games like CW said in a couple days, except when there is a high demand game in the top of my list. This then can take upto a week for the game to be sent out, but then I'm not too bothered about the wait as I've got enough unfinished games to be gettin on with.
You can purchase most games you rent, and they will send you the box and manual. Prices are usually on a par with the like of Amazon, Shopto.net, etc. I bought Just Cause 2 Limited Edition for £9.50 the other week. All the games I have bought from em have been in excellent condition.
There customer service is quite good, I've only had a couple of minor queries and they got back to me quickly. I got a free month rental out em once too.
I think they do a referral offer, it would be only fair to refer Wolf as he has been bangin on about this for a while now.
I rent films with Lovefilm, the only downside I found with there game rentals is that you can't purchase the game your are currently renting, which is surprising cos they are owned by Amazon.
I know Optikal uses Lovefilm and the only other forumite I can remember renting games is Dante.