Hi
Can You tel me differences between Ethernet shield based on ENC28J60 and "original" arduino wiznet Ethernet shield?
ENC28J60 is very cheap but is it good?
The ENC28J60 is a "bare" ethernet board. You have to implement any networking protocols (TCP/IP, etc) in firmware on the Arduino, which is relatively challenging when you only have 32k of code space and 2k of RAM.
The Wiznet chips used on the official ethernet board include both ethernet AND some sort of embedded CPU that does IP, UDP, and TCP for you (mostly), leaving more room in the arduino for actual application. (The cpu buried inside the Wiznet chip is probably bigger and more powerful than the arduino cpu...)
OK,
So if I'll use CPU with large RAM there will be no difference ?(in things that may be done) I'm talking about standard libraries for official and ENC28J60 . (i know that official lib is easier to use)
Can the page be loaded from EEPROM,sd or external mem?
I don't know about loading pages, but I do know that people have all sorts of problems with the ENC28J60 shield.
If you do a forum search for Ethernet shield, and look at threads where people are having problems, I'd say that 9 times out of 10 they're using the ENC28J60.
The Wiznet is more documented, tested, and overall used which leads to a LOT of sample scripts for doing pretty much anything you could ever want to do! 
I can see the appeal of the cheaper ENC28J60 shield (in fact, I almost bought one the other day because I saw it cheap), but in reality, you only save about $5-10 USD (here's the ENC28j60 for $24.95, and here's the Wiznet for $29.00).
I recommend you just save up the extra few bucks and go with what we all know works well :).
if I'll use CPU with large RAM there will be no difference ?
"Theoretically." In practice, there are no Arduino CPUs with that much RAM
I would look at reduced cost Wiznet-based modules before I looked at ENC28J60 modules, for most applications. For instance, you can get the core Wiznet module (SW compatible, but no "shield format") for about $21: http://www.ewiznet.com/goods_detail.php?goodsIdx=125
(adafruit has an shield adapter, but there goes most of te cost savings.)
And then there is the Seeedstudio version, and the random clones from China...
I bought a Ethernet Shield for my arduino from DFrobot. It's the same as a normal official Ethernet shield, but only cheaper, and another cooler color.
Pics in my most recent blogpost: http://coding-kid.tk