For me, Akismet is a must have... recently, I'm been getting bombarded with spam comments (~300-400 a day), though unfortunately, I've just got 130 in 12 hours (and counting) spam pingbacks from autoblogs on one post and they weren't caught by Akismet...
Other than Akismet, I find CommentLuv, NoFollow Free, All in One SEO, and Twitter Friendly Links extremely useful.
If you have any other WordPress site, from which you want to import your blogs.You can use this.
I am looking for a backup and restore plugin?
Because in free hosting services disaster can happen any time.I am creating blogs on my local host and don't know how to upload them properly.I can do restore local database and files on remote server to do that, but this is not a logical way I think for just to import blogs on remote server.
For backing up your database, try this:
http://x10hosting.com/wiki/How_to_Automatically_Backup_your_Database
If you want a plugin, you can try:
http://wordpress.org/extend/plugins/wp-db-backup/ but I've noticed this sometimes triggers a high resource suspension depending on your database size.