Have a look at the Baby Station www.babystation.com
My daughter has had one since she was 4 months and she is now 15 months. She doesn't sit in a lot now, but it still gets used every day while I get ready for work.
It was great when she couldn't sit up unaided, because she could reach her toys and was safe. Its been a godsend through the crawling stage, because she was into everything. You can use their own toys, which means they don't get restricted to static toys. Easy to clean, easy to store, great for the garden - its been a great entertainer/high chair/floor seat for us.