There’s a great app called FreeMemory that quickly frees up a lot of memory. It’s definitely worth the $0.99.
The last update adds a great feature that let’s you see all of the processes running on your phone.
Last night I started noticing that sometimes MobileSafari stays running as a background process. This only seems to occur if you close Safari with a web page open.
In these screenshots, you can see what I mean. The quick tip to save a lot of memory is to close any open pages before you quit Safari. I didn’t use the free memory button on this. I just closed the page between uses in Safari