What are some alternatives?
When comparing Domainr and Short Domain Search, you can also consider the following products
namegrep - Domain name search with regular expressions and curated sets
Agile Domain Search - Search great domain names for your website in seconds.
Undeveloped - Domains you never thought were available
Instant Domain Search - Search domain names instantly by showing results as you type.
Weird One Character Domain Superstore - Weird and available one character domain names
Lean Domain Search - Find a Great Domain Name w/ twitter handle availability